| Message ID | 20180721142035.21059-7-hjl.tools@gmail.com |
|---|---|
| State | New |
| Headers | show |
| Series | x86/CET: The last 12 patches to enable Intel CET | expand |
On 07/21/2018 10:20 AM, H.J. Lu wrote: > This patch adds a field to ucontext_t to save shadow stack: > > 1. getcontext and swapcontext are updated to save the caller's shadow > stack pointer and return addresses. > 2. setcontext and swapcontext are updated to restore shadow stack and > jump to new context directly. > 3. makecontext is updated to allocate a new shadow stack and set the > caller's return address to __start_context. > > Since makecontext allocates a new shadow stack when making a new > context and kernel allocates a new shadow stack for clone/fork/vfork > syscalls, we keep track the lowest shadow stack base. In setcontext > and swapcontext, when searching for shadow stack restore token, if the > lowest shadow stack base is reached, we assume both the current and > target shadow stack pointers are on the same shadow stack. > > We enable shadow stack at run-time only if program and all used shared > objects, including dlopened ones, are shadow stack enabled, which means > that they must be compiled with GCC 8 or above and glibc 2.28 or above. > We need to save and restore shadow stack only if shadow stack is enabled. > When caller of getcontext, setcontext, swapcontext and makecontext is > compiled with smaller ucontext_t, shadow stack won't be enabled at > run-time. We check if shadow stack is enabled before accessing the > extended field in ucontext_t. > Right, this is a flag day ABI change. > 2018-05-21 Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com> > H.J. Lu <hongjiu.lu@intel.com> > > * sysdeps/unix/sysv/linux/x86/sys/ucontext.h (ucontext_t): Add > __ssp. > * sysdeps/unix/sysv/linux/x86_64/__start_context.S: Include > <bits/prctl.h> and "ucontext_i.h" when shadow stack is enabled. > (__push___start_context): New. > * sysdeps/unix/sysv/linux/x86_64/getcontext.S (__getcontext): > Save the caller's shadow stack pointer when shadow stack is in > use. > * sysdeps/unix/sysv/linux/x86_64/makecontext.c Include > <pthread.h>, <libc-pointer-arith.h> and <sys/prctl.h>. > (__push___start_context): New prototype. > (__makecontext): Call __push___start_context to allocate a new > shadow stack, push __start_context onto the new stack as well > as the new shadow stack. Set the lowest shadow stack base. > * sysdeps/unix/sysv/linux/x86_64/setcontext.S: Include > <bits/prctl.h>. > (__setcontext): Use the restore token to restore shadow stack > if available. Otherwise unwind shadow stack. Check if the > target shadow stack pointer came from __push___start_context. > Don't search for shadow stack restore token below the lowest > shadow stack base. > * sysdeps/unix/sysv/linux/x86_64/swapcontext.S: Include > <bits/prctl.h>. > (__swapcontext): Save the current shadow stack pointer. > Use the restore token to restore shadow stack if available. > Otherwise unwind shadow stack. Check if the target shadow > stack pointer came from __push___start_context. Don't search > for shadow stack restore token below the lowest shadow stack > base. > * sysdeps/unix/sysv/linux/x86_64/sysdep.h > (STACK_SIZE_TO_SHADOW_STACK_SIZE_SHIFT): New. > * sysdeps/unix/sysv/linux/x86_64/ucontext_i.sym (oSSP): New. > --- OK for 2.28, but should we increase the size we allocate in the new structure? The hardest part to review was the CET token save/restore state transitions between context changes and for example I still don't clearly understand why we need to check if the restored state is on the same shadow stack and unwind? Is this because we are trying to unwind the shadow stack as often as possible to avoid overflow (as we do in the unwind_shadow_stack/loop sequence). Why do we do this unwind process? Reviewed-by: Carlos O'Donell <carlos@redhat.com> > sysdeps/unix/sysv/linux/x86/sys/ucontext.h | 2 + > .../unix/sysv/linux/x86_64/__start_context.S | 75 +++++++++ > sysdeps/unix/sysv/linux/x86_64/getcontext.S | 17 ++ > sysdeps/unix/sysv/linux/x86_64/makecontext.c | 56 ++++++- > sysdeps/unix/sysv/linux/x86_64/setcontext.S | 139 ++++++++++++++++ > sysdeps/unix/sysv/linux/x86_64/swapcontext.S | 150 ++++++++++++++++++ > sysdeps/unix/sysv/linux/x86_64/sysdep.h | 5 + > sysdeps/unix/sysv/linux/x86_64/ucontext_i.sym | 1 + > 8 files changed, 444 insertions(+), 1 deletion(-) > > diff --git a/sysdeps/unix/sysv/linux/x86/sys/ucontext.h b/sysdeps/unix/sysv/linux/x86/sys/ucontext.h > index afb7c181bf..7367726a50 100644 > --- a/sysdeps/unix/sysv/linux/x86/sys/ucontext.h > +++ b/sysdeps/unix/sysv/linux/x86/sys/ucontext.h > @@ -147,6 +147,7 @@ typedef struct ucontext_t > mcontext_t uc_mcontext; > sigset_t uc_sigmask; > struct _libc_fpstate __fpregs_mem; > + __extension__ unsigned long long int __ssp[4]; This is an ABI change, is this enough space for future changes also? Should we extend this to have some more space? > } ucontext_t; > > #else /* !__x86_64__ */ > @@ -251,6 +252,7 @@ typedef struct ucontext_t > mcontext_t uc_mcontext; > sigset_t uc_sigmask; > struct _libc_fpstate __fpregs_mem; > + unsigned long int __ssp[4]; Likewise. > } ucontext_t; > > #endif /* !__x86_64__ */ > diff --git a/sysdeps/unix/sysv/linux/x86_64/__start_context.S b/sysdeps/unix/sysv/linux/x86_64/__start_context.S > index 0bfde5fc31..01e672c09b 100644 > --- a/sysdeps/unix/sysv/linux/x86_64/__start_context.S > +++ b/sysdeps/unix/sysv/linux/x86_64/__start_context.S > @@ -18,6 +18,80 @@ > > #include <sysdep.h> > > +#if SHSTK_ENABLED > +# include <bits/prctl.h> > +# include "ucontext_i.h" > + > +/* Use CALL to push __start_context onto the new stack as well as the new > + shadow stack. RDI points to ucontext: > + Incoming: > + __ssp[0]: The original caller's shadow stack pointer. > + __ssp[1]: The size of the new shadow stack. > + __ssp[2]: The size of the new shadow stack. > + Outgoing: > + __ssp[0]: The new shadow stack pointer. > + __ssp[1]: The base address of the new shadow stack. > + __ssp[2]: The size of the new shadow stack. OK. > + */ OK. > + > +ENTRY(__push___start_context) > + /* Save the pointer to ucontext. */ > + movq %rdi, %r9 > + /* Get the original shadow stack pointer. */ > + rdsspq %r8 > + /* Save the original stack pointer. */ > + movq %rsp, %rdx > + /* Load the top of the new stack into RSI. */ > + movq oRSP(%rdi), %rsi > + /* Add 8 bytes to RSI since CALL will push the 8-byte return > + address onto stack. */ > + leaq 8(%rsi), %rsp > + /* Allocate the new shadow stack. The size of the new shadow > + stack is passed in __ssp[1]. */ > + lea (oSSP + 8)(%rdi), %RSI_LP > + movl $ARCH_CET_ALLOC_SHSTK, %edi > + movl $__NR_arch_prctl, %eax OK. > + /* The new shadow stack base is returned in __ssp[1]. */ > + syscall > + testq %rax, %rax > + jne L(hlt) /* This should never happen. */ > + > + /* Get the size of the new shadow stack. */ > + movq 8(%rsi), %rdi > + > + /* Get the base address of the new shadow stack. */ > + movq (%rsi), %rsi > + > + /* Use the restore stoken to restore the new shadow stack. */ > + rstorssp -8(%rsi, %rdi) OK. > + > + /* Save the restore token on the original shadow stack. */ > + saveprevssp > + > + /* Push the address of "jmp __start_context" onto the new stack > + as well as the new shadow stack. */ > + call 1f > + jmp __start_context OK. > +1: > + > + /* Get the new shadow stack pointer. */ > + rdsspq %rdi > + > + /* Use the restore stoken to restore the original shadow stack. */ > + rstorssp -8(%r8) > + > + /* Save the restore token on the new shadow stack. */ > + saveprevssp > + > + /* Store the new shadow stack pointer in __ssp[0]. */ > + movq %rdi, oSSP(%r9) > + > + /* Restore the original stack. */ > + mov %rdx, %rsp > + ret OK. > +END(__push___start_context) > +#endif > + > /* This is the helper code which gets called if a function which is > registered with 'makecontext' returns. In this case we have to > install the context listed in the uc_link element of the context > @@ -45,5 +119,6 @@ ENTRY(__start_context) > call HIDDEN_JUMPTARGET(exit) > /* The 'exit' call should never return. In case it does cause > the process to terminate. */ > +L(hlt): OK. > hlt > END(__start_context) > diff --git a/sysdeps/unix/sysv/linux/x86_64/getcontext.S b/sysdeps/unix/sysv/linux/x86_64/getcontext.S > index 33347bc02e..cbbe4cc9fc 100644 > --- a/sysdeps/unix/sysv/linux/x86_64/getcontext.S > +++ b/sysdeps/unix/sysv/linux/x86_64/getcontext.S > @@ -53,6 +53,23 @@ ENTRY(__getcontext) > leaq 8(%rsp), %rcx /* Exclude the return address. */ > movq %rcx, oRSP(%rdi) > > +#if SHSTK_ENABLED > + /* Check if shadow stack is enabled. */ > + testl $X86_FEATURE_1_SHSTK, %fs:FEATURE_1_OFFSET > + jz L(no_shstk) > + > + /* Get the current shadow stack pointer. */ > + rdsspq %rax > + /* NB: Save the caller's shadow stack so that we can jump back > + to the caller directly. */ > + addq $8, %rax > + movq %rax, oSSP(%rdi) > + xorl %edx, %edx > + movq %rdx, (oSSP + 8)(%rdi) > + movq %rdx, (oSSP + 16)(%rdi) OK, Save it. > + > +L(no_shstk): > +#endif > /* We have separate floating-point register content memory on the > stack. We use the __fpregs_mem block in the context. Set the > links up correctly. */ > diff --git a/sysdeps/unix/sysv/linux/x86_64/makecontext.c b/sysdeps/unix/sysv/linux/x86_64/makecontext.c > index 0d0802bf43..97f9bbbd2d 100644 > --- a/sysdeps/unix/sysv/linux/x86_64/makecontext.c > +++ b/sysdeps/unix/sysv/linux/x86_64/makecontext.c > @@ -21,6 +21,11 @@ > #include <stdarg.h> > #include <stdint.h> > #include <ucontext.h> > +#if SHSTK_ENABLED > +# include <pthread.h> > +# include <libc-pointer-arith.h> > +# include <sys/prctl.h> > +#endif OK (with prctl.h changes proposed by Joseph). > > #include "ucontext_i.h" > > @@ -52,6 +57,8 @@ void > __makecontext (ucontext_t *ucp, void (*func) (void), int argc, ...) > { > extern void __start_context (void) attribute_hidden; > + extern void __push___start_context (ucontext_t *) > + attribute_hidden; OK. > greg_t *sp; > unsigned int idx_uc_link; > va_list ap; > @@ -74,7 +81,54 @@ __makecontext (ucontext_t *ucp, void (*func) (void), int argc, ...) > ucp->uc_mcontext.gregs[REG_RSP] = (uintptr_t) sp; > > /* Setup stack. */ > - sp[0] = (uintptr_t) &__start_context; > +#if SHSTK_ENABLED > + struct pthread *self = THREAD_SELF; > + unsigned int feature_1 = THREAD_GETMEM (self, header.feature_1); > + /* NB: We must check feature_1 before accessing __ssp since caller > + may be compiled against ucontext_t without __ssp. */ OK. Correct, don't touch elements potentially outside of the ABI. > + if ((feature_1 & X86_FEATURE_1_SHSTK) != 0) > + { > + /* Shadow stack is enabled. We need to allocate a new shadow > + stack. */ > + unsigned long ssp_size = (((uintptr_t) sp > + - (uintptr_t) ucp->uc_stack.ss_sp) > + >> STACK_SIZE_TO_SHADOW_STACK_SIZE_SHIFT); > + /* Align shadow stack to 8 bytes. */ > + ssp_size = ALIGN_UP (ssp_size, 8); OK. > + > + ucp->__ssp[1] = ssp_size; > + ucp->__ssp[2] = ssp_size; OK. > + > + /* Call __push___start_context to allocate a new shadow stack, > + push __start_context onto the new stack as well as the new > + shadow stack. NB: After __push___start_context returns, > + ucp->__ssp[0]: The new shadow stack pointer. > + ucp->__ssp[1]: The base address of the new shadow stack. > + ucp->__ssp[2]: The size of the new shadow stack. > + */ > + __push___start_context (ucp); OK. > + > + /* Update the lowest shadow stack base. NB: Since a new shadow > + stack may be switch by clone syscall, we need to get the s/switch by clone/switched by the/g > + current default shadow stack base via ARCH_CET_STATUS. */ > + unsigned long long cet_status[3]; > + INTERNAL_SYSCALL_DECL (err); > + if (INTERNAL_SYSCALL (arch_prctl, err, 2, ARCH_CET_STATUS, > + cet_status) == 0) > + { > + unsigned long long new_ssp_base = ucp->__ssp[1]; > + if (new_ssp_base > cet_status[1]) > + new_ssp_base = cet_status[1]; > + > + unsigned long long current_ssp_base > + = THREAD_GETMEM (self, header.ssp_base); > + if (!current_ssp_base || current_ssp_base > new_ssp_base) > + THREAD_SETMEM (self, header.ssp_base, new_ssp_base); > + } OK. > + } > + else > +#endif > + sp[0] = (uintptr_t) &__start_context; OK. > sp[idx_uc_link] = (uintptr_t) ucp->uc_link; > > va_start (ap, argc); > diff --git a/sysdeps/unix/sysv/linux/x86_64/setcontext.S b/sysdeps/unix/sysv/linux/x86_64/setcontext.S > index b42af8e291..88c4df5e45 100644 > --- a/sysdeps/unix/sysv/linux/x86_64/setcontext.S > +++ b/sysdeps/unix/sysv/linux/x86_64/setcontext.S > @@ -18,6 +18,7 @@ > <http://www.gnu.org/licenses/>. */ > > #include <sysdep.h> > +#include <bits/prctl.h> OK, though this changes with Joseph's recommendations. > > #include "ucontext_i.h" > > @@ -79,6 +80,144 @@ ENTRY(__setcontext) > movq oR14(%rdx), %r14 > movq oR15(%rdx), %r15 > > +#if SHSTK_ENABLED > + /* Check if shadow stack is enabled. */ > + testl $X86_FEATURE_1_SHSTK, %fs:FEATURE_1_OFFSET > + jz L(no_shstk) > + OK. > + /* Get the base address and size of the default shadow stack. > + NB: We can't cache them since CLONE syscall switches the > + default shadow stack. */ > + sub $24, %RSP_LP > + mov %RSP_LP, %RSI_LP > + movl $ARCH_CET_STATUS, %edi > + movl $__NR_arch_prctl, %eax > + syscall > + testq %rax, %rax > + jne L(hlt) /* This should never happen. */ OK. > + > + /* Get the current shadow stack pointer. */ > + rdsspq %rcx > + OK. > + /* NB: If both the target shadow stack pointer and the current > + shadow stack pointer are on the original shadow stack, we > + can unwind the stack. Otherwise, find the restore token > + pushed by rstorssp and saveprevssp to restore the target > + shadow stack. */ > + movq oSSP(%rdx), %rdi > + movq %rdi, %rsi > + subq 8(%rsp), %rsi > + jb L(find_restore_token) > + cmpq 16(%rsp), %rsi > + jae L(find_restore_token) OK. > + > + /* Check if both shadow stack pointers are on the original > + shadow stack. */ > + movq %rcx, %rsi > + subq 8(%rsp), %rsi > + jb L(find_restore_token) > + cmpq 16(%rsp), %rsi > + jae L(find_restore_token) > + > + jmp L(unwind_shadow_stack) > + OK. > +L(find_restore_token): > + /* Save the target shadow stack pointer. */ > + movq %rdi, %rsi > + > + /* Check if the target shadow stack pointer came from > + __push___start_context. */ > + movq (%rsi), %rax > + andq $-8, %rax > + leaq 8(%rsi), %r8 > + cmpq %r8, %rax > + jne L(skip_restore_shadow_stack_special) OK. > + > + /* Pop return address from the shadow stack since setcontext > + will not return. */ > + movq $1, %rax > + incsspq %rax > + > + /* Use the restore stoken to restore the target shadow stack. */ > + rstorssp (%rsi) OK. > + > + jmp L(unwind_shadow_stack_special) > + > +L(skip_restore_shadow_stack_special): > + movq %fs:SSP_BASE_OFFSET, %r8 > +L(find_restore_token_loop): > + /* Check if there is a restore token. */ > + movq -8(%rsi), %rax > + andq $-8, %rax > + cmpq %rsi, %rax > + je L(restore_shadow_stack) > + > + /* Try the next slot. */ > + subq $8, %rsi > + > + /* Don't check restore token below the lowest shadow stack > + base. */ > + cmpq %r8, %rsi > + ja L(find_restore_token_loop) OK. > + > + jmp L(unwind_shadow_stack) > + > +L(restore_shadow_stack): > + /* Pop return address from the shadow stack since setcontext > + will not return. */ > + movq $1, %rax > + incsspq %rax > + > + /* Use the restore stoken to restore the target shadow stack. */ > + rstorssp -8(%rsi) > + > + /* Save the restore token on the old shadow stack. NB: This > + restore token may be checked by setcontext or swapcontext > + later. */ > + saveprevssp OK. > + > +L(unwind_shadow_stack_special): > + /* Get the current shadow stack. */ > + rdsspq %rcx > + > +L(unwind_shadow_stack): > + add $24, %RSP_LP > + /* Unwind the shadow stack. */ > + subq %rdi, %rcx > + je L(skip_unwind_shadow_stack) > + negq %rcx > + shrq $3, %rcx > + movl $255, %esi > +L(loop): > + cmpq %rsi, %rcx > + cmovb %rcx, %rsi > + incsspq %rsi > + subq %rsi, %rcx > + ja L(loop) Unwind the shadow stack. > + > +L(skip_unwind_shadow_stack): > + movq oRSI(%rdx), %rsi > + movq oRDI(%rdx), %rdi > + movq oRCX(%rdx), %rcx > + movq oR8(%rdx), %r8 > + movq oR9(%rdx), %r9 > + > + /* Get the return address set with getcontext. */ > + movq oRIP(%rdx), %r10 > + > + /* Setup finally %rdx. */ > + movq oRDX(%rdx), %rdx > + > + /* Clear rax to indicate success. */ > + xorl %eax, %eax > + /* Jump to the new context directly. */ > + jmp *%r10 > + > +L(hlt): > + hlt > + > +L(no_shstk): OK. > +#endif > /* The following ret should return to the address set with > getcontext. Therefore push the address on the stack. */ > movq oRIP(%rdx), %rcx > diff --git a/sysdeps/unix/sysv/linux/x86_64/swapcontext.S b/sysdeps/unix/sysv/linux/x86_64/swapcontext.S > index 1110c479fa..7a47275727 100644 > --- a/sysdeps/unix/sysv/linux/x86_64/swapcontext.S > +++ b/sysdeps/unix/sysv/linux/x86_64/swapcontext.S > @@ -18,6 +18,7 @@ > <http://www.gnu.org/licenses/>. */ > > #include <sysdep.h> > +#include <bits/prctl.h> OK (modulo name change). > > #include "ucontext_i.h" > > @@ -67,6 +68,7 @@ ENTRY(__swapcontext) > > /* The syscall destroys some registers, save them. */ > movq %rsi, %r12 > + movq %rdi, %r9 OK. > > /* Save the current signal mask and install the new one with > rt_sigprocmask (SIG_BLOCK, newset, oldset,_NSIG/8). */ > @@ -99,6 +101,154 @@ ENTRY(__swapcontext) > movq oR14(%rdx), %r14 > movq oR15(%rdx), %r15 > > +#if SHSTK_ENABLED > + /* Check if shadow stack is enabled. */ > + testl $X86_FEATURE_1_SHSTK, %fs:FEATURE_1_OFFSET > + jz L(no_shstk) OK. > + > + /* Get the base address and size of the default shadow stack. > + NB: We can't cache them since CLONE syscall switches the > + default shadow stack. */ > + sub $24, %RSP_LP > + mov %RSP_LP, %RSI_LP > + movl $ARCH_CET_STATUS, %edi > + movl $__NR_arch_prctl, %eax > + syscall > + testq %rax, %rax > + jne L(hlt) /* This should never happen. */ OK. > + > + /* Get the current shadow stack pointer. */ > + rdsspq %rcx > + > + /* On the original shadow stack, save the caller's shadow > + stack so that we can jump back to the caller directly. */ > + leaq 8(%rcx), %rsi > + > + /* Save the current shadow stack pointer in __ssp[0]. */ > + movq %rsi, oSSP(%r9) > + > + /* NB: If both the target shadow stack pointer and the current > + shadow stack pointer are on the original shadow stack, we > + can unwind the stack. Otherwise, find the restore token > + pushed by rstorssp and saveprevssp to restore the target > + shadow stack. */ OK. > + movq oSSP(%rdx), %rdi > + movq %rdi, %rsi > + subq 8(%rsp), %rsi > + jb L(find_restore_token) > + cmpq 16(%rsp), %rsi > + jae L(find_restore_token) > + > + /* Check if both shadow stack pointers are on the original > + shadow stack. */ > + movq %rcx, %rsi > + subq 8(%rsp), %rsi > + jb L(find_restore_token) > + cmpq 16(%rsp), %rsi > + jae L(find_restore_token) > + > + jmp L(unwind_shadow_stack) > + > +L(find_restore_token): > + /* Save the target shadow stack pointer. */ > + movq %rdi, %rsi > + > + /* Check if the target shadow stack pointer came from > + __push___start_context. */ > + movq (%rsi), %rax > + andq $-8, %rax > + leaq 8(%rsi), %r8 > + cmpq %r8, %rax > + jne L(skip_restore_shadow_stack_special) > + > + /* Pop return address from the shadow stack since setcontext > + will not return. */ > + movq $1, %rax > + incsspq %rax OK. > + > + /* Use the restore stoken to restore the target shadow stack. */ > + rstorssp (%rsi) OK. > + > + jmp L(unwind_shadow_stack_special) > + > +L(skip_restore_shadow_stack_special): > + movq %fs:SSP_BASE_OFFSET, %r8 OK. > +L(find_restore_token_loop): > + /* Check if there is a restore token. */ > + movq -8(%rsi), %rax > + andq $-8, %rax > + cmpq %rsi, %rax > + je L(restore_shadow_stack) > + > + /* Try the next slot. */ > + subq $8, %rsi > + > + /* Don't check restore token below the lowest shadow stack > + base. */ > + cmpq %r8, %rsi > + ja L(find_restore_token_loop) > + > + jmp L(unwind_shadow_stack) > + > +L(restore_shadow_stack): > + /* Pop return address from the shadow stack since setcontext > + will not return. */ > + movq $1, %rax > + incsspq %rax > + > + /* Restore the target shadow stack. */ > + rstorssp -8(%rsi) > + > +L(unwind_shadow_stack_special): > + /* Save restore token on the old shadow stack. */ > + saveprevssp > + > + /* Get the current shadow stack. */ > + rdsspq %rcx > + > +L(unwind_shadow_stack): > + add $24, %RSP_LP > + /* Unwind the shadow stack. */ > + subq %rdi, %rcx > + je L(skip_unwind_shadow_stack) > + negq %rcx > + shrq $3, %rcx > + movl $255, %esi OK. > +L(loop): > + cmpq %rsi, %rcx > + cmovb %rcx, %rsi > + incsspq %rsi > + subq %rsi, %rcx > + ja L(loop) OK. Unwind and keep unwinding. > + > +L(skip_unwind_shadow_stack): > + xorl %eax, %eax > + movq %rax, (oSSP + 8)(%r9) > + movq %rax, (oSSP + 16)(%r9) > + > + /* Setup registers used for passing args. */ > + movq oRDI(%rdx), %rdi > + movq oRSI(%rdx), %rsi > + movq oRCX(%rdx), %rcx > + movq oR8(%rdx), %r8 > + movq oR9(%rdx), %r9 > + > + /* Get the return address set with getcontext. */ > + movq oRIP(%rdx), %r10 > + > + /* Setup finally %rdx. */ > + movq oRDX(%rdx), %rdx > + > + /* Clear rax to indicate success. */ > + xorl %eax, %eax > + /* Jump to the new context directly. */ > + jmp *%r10 OK. > + > +L(hlt): > + hlt > + > +L(no_shstk): > +#endif > /* The following ret should return to the address set with > getcontext. Therefore push the address on the stack. */ > movq oRIP(%rdx), %rcx > diff --git a/sysdeps/unix/sysv/linux/x86_64/sysdep.h b/sysdeps/unix/sysv/linux/x86_64/sysdep.h > index 1ef0f742ae..f07eb04962 100644 > --- a/sysdeps/unix/sysv/linux/x86_64/sysdep.h > +++ b/sysdeps/unix/sysv/linux/x86_64/sysdep.h > @@ -423,4 +423,9 @@ > #undef LO_HI_LONG > #define LO_HI_LONG(val) (val), 0 > > +/* Each shadow stack slot takes 8 bytes. Assuming that each stack > + frame takes 256 bytes, this is used to compute shadow stack size > + from stack size. */ > +#define STACK_SIZE_TO_SHADOW_STACK_SIZE_SHIFT 5 OK. > + > #endif /* linux/x86_64/sysdep.h */ > diff --git a/sysdeps/unix/sysv/linux/x86_64/ucontext_i.sym b/sysdeps/unix/sysv/linux/x86_64/ucontext_i.sym > index af3e0e544b..c08b3b8b47 100644 > --- a/sysdeps/unix/sysv/linux/x86_64/ucontext_i.sym > +++ b/sysdeps/unix/sysv/linux/x86_64/ucontext_i.sym > @@ -35,3 +35,4 @@ oFPREGS mcontext (fpregs) > oSIGMASK ucontext (uc_sigmask) > oFPREGSMEM ucontext (__fpregs_mem) > oMXCSR ucontext (__fpregs_mem.mxcsr) > +oSSP ucontext (__ssp) OK. > Cheers, Carlos.
diff --git a/sysdeps/unix/sysv/linux/x86/sys/ucontext.h b/sysdeps/unix/sysv/linux/x86/sys/ucontext.h index afb7c181bf..7367726a50 100644 --- a/sysdeps/unix/sysv/linux/x86/sys/ucontext.h +++ b/sysdeps/unix/sysv/linux/x86/sys/ucontext.h @@ -147,6 +147,7 @@ typedef struct ucontext_t mcontext_t uc_mcontext; sigset_t uc_sigmask; struct _libc_fpstate __fpregs_mem; + __extension__ unsigned long long int __ssp[4]; } ucontext_t; #else /* !__x86_64__ */ @@ -251,6 +252,7 @@ typedef struct ucontext_t mcontext_t uc_mcontext; sigset_t uc_sigmask; struct _libc_fpstate __fpregs_mem; + unsigned long int __ssp[4]; } ucontext_t; #endif /* !__x86_64__ */ diff --git a/sysdeps/unix/sysv/linux/x86_64/__start_context.S b/sysdeps/unix/sysv/linux/x86_64/__start_context.S index 0bfde5fc31..01e672c09b 100644 --- a/sysdeps/unix/sysv/linux/x86_64/__start_context.S +++ b/sysdeps/unix/sysv/linux/x86_64/__start_context.S @@ -18,6 +18,80 @@ #include <sysdep.h> +#if SHSTK_ENABLED +# include <bits/prctl.h> +# include "ucontext_i.h" + +/* Use CALL to push __start_context onto the new stack as well as the new + shadow stack. RDI points to ucontext: + Incoming: + __ssp[0]: The original caller's shadow stack pointer. + __ssp[1]: The size of the new shadow stack. + __ssp[2]: The size of the new shadow stack. + Outgoing: + __ssp[0]: The new shadow stack pointer. + __ssp[1]: The base address of the new shadow stack. + __ssp[2]: The size of the new shadow stack. + */ + +ENTRY(__push___start_context) + /* Save the pointer to ucontext. */ + movq %rdi, %r9 + /* Get the original shadow stack pointer. */ + rdsspq %r8 + /* Save the original stack pointer. */ + movq %rsp, %rdx + /* Load the top of the new stack into RSI. */ + movq oRSP(%rdi), %rsi + /* Add 8 bytes to RSI since CALL will push the 8-byte return + address onto stack. */ + leaq 8(%rsi), %rsp + /* Allocate the new shadow stack. The size of the new shadow + stack is passed in __ssp[1]. */ + lea (oSSP + 8)(%rdi), %RSI_LP + movl $ARCH_CET_ALLOC_SHSTK, %edi + movl $__NR_arch_prctl, %eax + /* The new shadow stack base is returned in __ssp[1]. */ + syscall + testq %rax, %rax + jne L(hlt) /* This should never happen. */ + + /* Get the size of the new shadow stack. */ + movq 8(%rsi), %rdi + + /* Get the base address of the new shadow stack. */ + movq (%rsi), %rsi + + /* Use the restore stoken to restore the new shadow stack. */ + rstorssp -8(%rsi, %rdi) + + /* Save the restore token on the original shadow stack. */ + saveprevssp + + /* Push the address of "jmp __start_context" onto the new stack + as well as the new shadow stack. */ + call 1f + jmp __start_context +1: + + /* Get the new shadow stack pointer. */ + rdsspq %rdi + + /* Use the restore stoken to restore the original shadow stack. */ + rstorssp -8(%r8) + + /* Save the restore token on the new shadow stack. */ + saveprevssp + + /* Store the new shadow stack pointer in __ssp[0]. */ + movq %rdi, oSSP(%r9) + + /* Restore the original stack. */ + mov %rdx, %rsp + ret +END(__push___start_context) +#endif + /* This is the helper code which gets called if a function which is registered with 'makecontext' returns. In this case we have to install the context listed in the uc_link element of the context @@ -45,5 +119,6 @@ ENTRY(__start_context) call HIDDEN_JUMPTARGET(exit) /* The 'exit' call should never return. In case it does cause the process to terminate. */ +L(hlt): hlt END(__start_context) diff --git a/sysdeps/unix/sysv/linux/x86_64/getcontext.S b/sysdeps/unix/sysv/linux/x86_64/getcontext.S index 33347bc02e..cbbe4cc9fc 100644 --- a/sysdeps/unix/sysv/linux/x86_64/getcontext.S +++ b/sysdeps/unix/sysv/linux/x86_64/getcontext.S @@ -53,6 +53,23 @@ ENTRY(__getcontext) leaq 8(%rsp), %rcx /* Exclude the return address. */ movq %rcx, oRSP(%rdi) +#if SHSTK_ENABLED + /* Check if shadow stack is enabled. */ + testl $X86_FEATURE_1_SHSTK, %fs:FEATURE_1_OFFSET + jz L(no_shstk) + + /* Get the current shadow stack pointer. */ + rdsspq %rax + /* NB: Save the caller's shadow stack so that we can jump back + to the caller directly. */ + addq $8, %rax + movq %rax, oSSP(%rdi) + xorl %edx, %edx + movq %rdx, (oSSP + 8)(%rdi) + movq %rdx, (oSSP + 16)(%rdi) + +L(no_shstk): +#endif /* We have separate floating-point register content memory on the stack. We use the __fpregs_mem block in the context. Set the links up correctly. */ diff --git a/sysdeps/unix/sysv/linux/x86_64/makecontext.c b/sysdeps/unix/sysv/linux/x86_64/makecontext.c index 0d0802bf43..97f9bbbd2d 100644 --- a/sysdeps/unix/sysv/linux/x86_64/makecontext.c +++ b/sysdeps/unix/sysv/linux/x86_64/makecontext.c @@ -21,6 +21,11 @@ #include <stdarg.h> #include <stdint.h> #include <ucontext.h> +#if SHSTK_ENABLED +# include <pthread.h> +# include <libc-pointer-arith.h> +# include <sys/prctl.h> +#endif #include "ucontext_i.h" @@ -52,6 +57,8 @@ void __makecontext (ucontext_t *ucp, void (*func) (void), int argc, ...) { extern void __start_context (void) attribute_hidden; + extern void __push___start_context (ucontext_t *) + attribute_hidden; greg_t *sp; unsigned int idx_uc_link; va_list ap; @@ -74,7 +81,54 @@ __makecontext (ucontext_t *ucp, void (*func) (void), int argc, ...) ucp->uc_mcontext.gregs[REG_RSP] = (uintptr_t) sp; /* Setup stack. */ - sp[0] = (uintptr_t) &__start_context; +#if SHSTK_ENABLED + struct pthread *self = THREAD_SELF; + unsigned int feature_1 = THREAD_GETMEM (self, header.feature_1); + /* NB: We must check feature_1 before accessing __ssp since caller + may be compiled against ucontext_t without __ssp. */ + if ((feature_1 & X86_FEATURE_1_SHSTK) != 0) + { + /* Shadow stack is enabled. We need to allocate a new shadow + stack. */ + unsigned long ssp_size = (((uintptr_t) sp + - (uintptr_t) ucp->uc_stack.ss_sp) + >> STACK_SIZE_TO_SHADOW_STACK_SIZE_SHIFT); + /* Align shadow stack to 8 bytes. */ + ssp_size = ALIGN_UP (ssp_size, 8); + + ucp->__ssp[1] = ssp_size; + ucp->__ssp[2] = ssp_size; + + /* Call __push___start_context to allocate a new shadow stack, + push __start_context onto the new stack as well as the new + shadow stack. NB: After __push___start_context returns, + ucp->__ssp[0]: The new shadow stack pointer. + ucp->__ssp[1]: The base address of the new shadow stack. + ucp->__ssp[2]: The size of the new shadow stack. + */ + __push___start_context (ucp); + + /* Update the lowest shadow stack base. NB: Since a new shadow + stack may be switch by clone syscall, we need to get the + current default shadow stack base via ARCH_CET_STATUS. */ + unsigned long long cet_status[3]; + INTERNAL_SYSCALL_DECL (err); + if (INTERNAL_SYSCALL (arch_prctl, err, 2, ARCH_CET_STATUS, + cet_status) == 0) + { + unsigned long long new_ssp_base = ucp->__ssp[1]; + if (new_ssp_base > cet_status[1]) + new_ssp_base = cet_status[1]; + + unsigned long long current_ssp_base + = THREAD_GETMEM (self, header.ssp_base); + if (!current_ssp_base || current_ssp_base > new_ssp_base) + THREAD_SETMEM (self, header.ssp_base, new_ssp_base); + } + } + else +#endif + sp[0] = (uintptr_t) &__start_context; sp[idx_uc_link] = (uintptr_t) ucp->uc_link; va_start (ap, argc); diff --git a/sysdeps/unix/sysv/linux/x86_64/setcontext.S b/sysdeps/unix/sysv/linux/x86_64/setcontext.S index b42af8e291..88c4df5e45 100644 --- a/sysdeps/unix/sysv/linux/x86_64/setcontext.S +++ b/sysdeps/unix/sysv/linux/x86_64/setcontext.S @@ -18,6 +18,7 @@ <http://www.gnu.org/licenses/>. */ #include <sysdep.h> +#include <bits/prctl.h> #include "ucontext_i.h" @@ -79,6 +80,144 @@ ENTRY(__setcontext) movq oR14(%rdx), %r14 movq oR15(%rdx), %r15 +#if SHSTK_ENABLED + /* Check if shadow stack is enabled. */ + testl $X86_FEATURE_1_SHSTK, %fs:FEATURE_1_OFFSET + jz L(no_shstk) + + /* Get the base address and size of the default shadow stack. + NB: We can't cache them since CLONE syscall switches the + default shadow stack. */ + sub $24, %RSP_LP + mov %RSP_LP, %RSI_LP + movl $ARCH_CET_STATUS, %edi + movl $__NR_arch_prctl, %eax + syscall + testq %rax, %rax + jne L(hlt) /* This should never happen. */ + + /* Get the current shadow stack pointer. */ + rdsspq %rcx + + /* NB: If both the target shadow stack pointer and the current + shadow stack pointer are on the original shadow stack, we + can unwind the stack. Otherwise, find the restore token + pushed by rstorssp and saveprevssp to restore the target + shadow stack. */ + movq oSSP(%rdx), %rdi + movq %rdi, %rsi + subq 8(%rsp), %rsi + jb L(find_restore_token) + cmpq 16(%rsp), %rsi + jae L(find_restore_token) + + /* Check if both shadow stack pointers are on the original + shadow stack. */ + movq %rcx, %rsi + subq 8(%rsp), %rsi + jb L(find_restore_token) + cmpq 16(%rsp), %rsi + jae L(find_restore_token) + + jmp L(unwind_shadow_stack) + +L(find_restore_token): + /* Save the target shadow stack pointer. */ + movq %rdi, %rsi + + /* Check if the target shadow stack pointer came from + __push___start_context. */ + movq (%rsi), %rax + andq $-8, %rax + leaq 8(%rsi), %r8 + cmpq %r8, %rax + jne L(skip_restore_shadow_stack_special) + + /* Pop return address from the shadow stack since setcontext + will not return. */ + movq $1, %rax + incsspq %rax + + /* Use the restore stoken to restore the target shadow stack. */ + rstorssp (%rsi) + + jmp L(unwind_shadow_stack_special) + +L(skip_restore_shadow_stack_special): + movq %fs:SSP_BASE_OFFSET, %r8 +L(find_restore_token_loop): + /* Check if there is a restore token. */ + movq -8(%rsi), %rax + andq $-8, %rax + cmpq %rsi, %rax + je L(restore_shadow_stack) + + /* Try the next slot. */ + subq $8, %rsi + + /* Don't check restore token below the lowest shadow stack + base. */ + cmpq %r8, %rsi + ja L(find_restore_token_loop) + + jmp L(unwind_shadow_stack) + +L(restore_shadow_stack): + /* Pop return address from the shadow stack since setcontext + will not return. */ + movq $1, %rax + incsspq %rax + + /* Use the restore stoken to restore the target shadow stack. */ + rstorssp -8(%rsi) + + /* Save the restore token on the old shadow stack. NB: This + restore token may be checked by setcontext or swapcontext + later. */ + saveprevssp + +L(unwind_shadow_stack_special): + /* Get the current shadow stack. */ + rdsspq %rcx + +L(unwind_shadow_stack): + add $24, %RSP_LP + /* Unwind the shadow stack. */ + subq %rdi, %rcx + je L(skip_unwind_shadow_stack) + negq %rcx + shrq $3, %rcx + movl $255, %esi +L(loop): + cmpq %rsi, %rcx + cmovb %rcx, %rsi + incsspq %rsi + subq %rsi, %rcx + ja L(loop) + +L(skip_unwind_shadow_stack): + movq oRSI(%rdx), %rsi + movq oRDI(%rdx), %rdi + movq oRCX(%rdx), %rcx + movq oR8(%rdx), %r8 + movq oR9(%rdx), %r9 + + /* Get the return address set with getcontext. */ + movq oRIP(%rdx), %r10 + + /* Setup finally %rdx. */ + movq oRDX(%rdx), %rdx + + /* Clear rax to indicate success. */ + xorl %eax, %eax + /* Jump to the new context directly. */ + jmp *%r10 + +L(hlt): + hlt + +L(no_shstk): +#endif /* The following ret should return to the address set with getcontext. Therefore push the address on the stack. */ movq oRIP(%rdx), %rcx diff --git a/sysdeps/unix/sysv/linux/x86_64/swapcontext.S b/sysdeps/unix/sysv/linux/x86_64/swapcontext.S index 1110c479fa..7a47275727 100644 --- a/sysdeps/unix/sysv/linux/x86_64/swapcontext.S +++ b/sysdeps/unix/sysv/linux/x86_64/swapcontext.S @@ -18,6 +18,7 @@ <http://www.gnu.org/licenses/>. */ #include <sysdep.h> +#include <bits/prctl.h> #include "ucontext_i.h" @@ -67,6 +68,7 @@ ENTRY(__swapcontext) /* The syscall destroys some registers, save them. */ movq %rsi, %r12 + movq %rdi, %r9 /* Save the current signal mask and install the new one with rt_sigprocmask (SIG_BLOCK, newset, oldset,_NSIG/8). */ @@ -99,6 +101,154 @@ ENTRY(__swapcontext) movq oR14(%rdx), %r14 movq oR15(%rdx), %r15 +#if SHSTK_ENABLED + /* Check if shadow stack is enabled. */ + testl $X86_FEATURE_1_SHSTK, %fs:FEATURE_1_OFFSET + jz L(no_shstk) + + /* Get the base address and size of the default shadow stack. + NB: We can't cache them since CLONE syscall switches the + default shadow stack. */ + sub $24, %RSP_LP + mov %RSP_LP, %RSI_LP + movl $ARCH_CET_STATUS, %edi + movl $__NR_arch_prctl, %eax + syscall + testq %rax, %rax + jne L(hlt) /* This should never happen. */ + + /* Get the current shadow stack pointer. */ + rdsspq %rcx + + /* On the original shadow stack, save the caller's shadow + stack so that we can jump back to the caller directly. */ + leaq 8(%rcx), %rsi + + /* Save the current shadow stack pointer in __ssp[0]. */ + movq %rsi, oSSP(%r9) + + /* NB: If both the target shadow stack pointer and the current + shadow stack pointer are on the original shadow stack, we + can unwind the stack. Otherwise, find the restore token + pushed by rstorssp and saveprevssp to restore the target + shadow stack. */ + movq oSSP(%rdx), %rdi + movq %rdi, %rsi + subq 8(%rsp), %rsi + jb L(find_restore_token) + cmpq 16(%rsp), %rsi + jae L(find_restore_token) + + /* Check if both shadow stack pointers are on the original + shadow stack. */ + movq %rcx, %rsi + subq 8(%rsp), %rsi + jb L(find_restore_token) + cmpq 16(%rsp), %rsi + jae L(find_restore_token) + + jmp L(unwind_shadow_stack) + +L(find_restore_token): + /* Save the target shadow stack pointer. */ + movq %rdi, %rsi + + /* Check if the target shadow stack pointer came from + __push___start_context. */ + movq (%rsi), %rax + andq $-8, %rax + leaq 8(%rsi), %r8 + cmpq %r8, %rax + jne L(skip_restore_shadow_stack_special) + + /* Pop return address from the shadow stack since setcontext + will not return. */ + movq $1, %rax + incsspq %rax + + /* Use the restore stoken to restore the target shadow stack. */ + rstorssp (%rsi) + + jmp L(unwind_shadow_stack_special) + +L(skip_restore_shadow_stack_special): + movq %fs:SSP_BASE_OFFSET, %r8 +L(find_restore_token_loop): + /* Check if there is a restore token. */ + movq -8(%rsi), %rax + andq $-8, %rax + cmpq %rsi, %rax + je L(restore_shadow_stack) + + /* Try the next slot. */ + subq $8, %rsi + + /* Don't check restore token below the lowest shadow stack + base. */ + cmpq %r8, %rsi + ja L(find_restore_token_loop) + + jmp L(unwind_shadow_stack) + +L(restore_shadow_stack): + /* Pop return address from the shadow stack since setcontext + will not return. */ + movq $1, %rax + incsspq %rax + + /* Restore the target shadow stack. */ + rstorssp -8(%rsi) + +L(unwind_shadow_stack_special): + /* Save restore token on the old shadow stack. */ + saveprevssp + + /* Get the current shadow stack. */ + rdsspq %rcx + +L(unwind_shadow_stack): + add $24, %RSP_LP + /* Unwind the shadow stack. */ + subq %rdi, %rcx + je L(skip_unwind_shadow_stack) + negq %rcx + shrq $3, %rcx + movl $255, %esi +L(loop): + cmpq %rsi, %rcx + cmovb %rcx, %rsi + incsspq %rsi + subq %rsi, %rcx + ja L(loop) + +L(skip_unwind_shadow_stack): + xorl %eax, %eax + movq %rax, (oSSP + 8)(%r9) + movq %rax, (oSSP + 16)(%r9) + + /* Setup registers used for passing args. */ + movq oRDI(%rdx), %rdi + movq oRSI(%rdx), %rsi + movq oRCX(%rdx), %rcx + movq oR8(%rdx), %r8 + movq oR9(%rdx), %r9 + + /* Get the return address set with getcontext. */ + movq oRIP(%rdx), %r10 + + /* Setup finally %rdx. */ + movq oRDX(%rdx), %rdx + + /* Clear rax to indicate success. */ + xorl %eax, %eax + /* Jump to the new context directly. */ + jmp *%r10 + +L(hlt): + hlt + +L(no_shstk): +#endif /* The following ret should return to the address set with getcontext. Therefore push the address on the stack. */ movq oRIP(%rdx), %rcx diff --git a/sysdeps/unix/sysv/linux/x86_64/sysdep.h b/sysdeps/unix/sysv/linux/x86_64/sysdep.h index 1ef0f742ae..f07eb04962 100644 --- a/sysdeps/unix/sysv/linux/x86_64/sysdep.h +++ b/sysdeps/unix/sysv/linux/x86_64/sysdep.h @@ -423,4 +423,9 @@ #undef LO_HI_LONG #define LO_HI_LONG(val) (val), 0 +/* Each shadow stack slot takes 8 bytes. Assuming that each stack + frame takes 256 bytes, this is used to compute shadow stack size + from stack size. */ +#define STACK_SIZE_TO_SHADOW_STACK_SIZE_SHIFT 5 + #endif /* linux/x86_64/sysdep.h */ diff --git a/sysdeps/unix/sysv/linux/x86_64/ucontext_i.sym b/sysdeps/unix/sysv/linux/x86_64/ucontext_i.sym index af3e0e544b..c08b3b8b47 100644 --- a/sysdeps/unix/sysv/linux/x86_64/ucontext_i.sym +++ b/sysdeps/unix/sysv/linux/x86_64/ucontext_i.sym @@ -35,3 +35,4 @@ oFPREGS mcontext (fpregs) oSIGMASK ucontext (uc_sigmask) oFPREGSMEM ucontext (__fpregs_mem) oMXCSR ucontext (__fpregs_mem.mxcsr) +oSSP ucontext (__ssp)