Message ID | 20201013175146.58558-1-hjl.tools@gmail.com |
---|---|
State | New |
Headers | show |
Series | x86/CET: Update vfork to prevent child return | expand |
On Tue, Oct 13, 2020 at 10:51 AM H.J. Lu <hjl.tools@gmail.com> wrote: > > Child of vfork should either call _exit or one of the exec family of > functions. But normally there is nothing to prevent child of vfork from > return of the vfork-calling function. Simpilfy x86 vfork when shadow > stack is in use to introduce mismatched shadow stack in child of vfork > to trigger SIGSEGV when the child returns from the function in which > vfork was called. I will check it in tomorrow if there are no objections. > --- > sysdeps/unix/sysv/linux/i386/vfork.S | 55 +++--------- > sysdeps/unix/sysv/linux/x86/Makefile | 5 ++ > sysdeps/unix/sysv/linux/x86/tst-cet-vfork-1.c | 88 +++++++++++++++++++ > sysdeps/unix/sysv/linux/x86_64/vfork.S | 36 +++----- > 4 files changed, 113 insertions(+), 71 deletions(-) > create mode 100644 sysdeps/unix/sysv/linux/x86/tst-cet-vfork-1.c > > diff --git a/sysdeps/unix/sysv/linux/i386/vfork.S b/sysdeps/unix/sysv/linux/i386/vfork.S > index ceb41db0bd..91277a639f 100644 > --- a/sysdeps/unix/sysv/linux/i386/vfork.S > +++ b/sysdeps/unix/sysv/linux/i386/vfork.S > @@ -21,39 +21,6 @@ > #include <bits/errno.h> > #include <tcb-offsets.h> > > -#if SHSTK_ENABLED > -/* The shadow stack prevents us from pushing the saved return PC onto > - the stack and returning normally. Instead we pop the shadow stack > - and return directly. This is the safest way to return and ensures > - any stack manipulations done by the vfork'd child doesn't cause the > - parent to terminate when CET is enabled. */ > -# undef SYSCALL_ERROR_HANDLER > -# ifdef PIC > -# define SYSCALL_ERROR_HANDLER \ > -0: \ > - calll .L1; \ > -.L1: \ > - popl %edx; \ > -.L2: \ > - addl $_GLOBAL_OFFSET_TABLE_ + (.L2 - .L1), %edx; \ > - movl __libc_errno@gotntpoff(%edx), %edx; \ > - negl %eax; \ > - movl %eax, %gs:(%edx); \ > - orl $-1, %eax; \ > - jmp 1b; > -# else > -# define SYSCALL_ERROR_HANDLER \ > -0: \ > - movl __libc_errno@indntpoff, %edx; \ > - negl %eax; \ > - movl %eax, %gs:(%edx); \ > - orl $-1, %eax; \ > - jmp 1b; > -# endif > -# undef SYSCALL_ERROR_LABEL > -# define SYSCALL_ERROR_LABEL 0f > -#endif > - > /* Clone the calling process, but without copying the whole address space. > The calling process is suspended until the new process exits or is > replaced by a call to `execve'. Return -1 for errors, 0 to the new process, > @@ -70,20 +37,17 @@ ENTRY (__vfork) > movl $SYS_ify (vfork), %eax > int $0x80 > > -#if !SHSTK_ENABLED > /* Jump to the return PC. Don't jump directly since this > disturbs the branch target cache. Instead push the return > address back on the stack. */ > pushl %ecx > cfi_adjust_cfa_offset (4) > -#endif > > cmpl $-4095, %eax > /* Branch forward if it failed. */ > jae SYSCALL_ERROR_LABEL > > #if SHSTK_ENABLED > -1: > /* Check if shadow stack is in use. */ > xorl %edx, %edx > rdsspd %edx > @@ -91,18 +55,19 @@ ENTRY (__vfork) > /* Normal return if shadow stack isn't in use. */ > je L(no_shstk) > > - /* Pop return address from shadow stack and jump back to caller > - directly. */ > - movl $1, %edx > - incsspd %edx > + testl %eax, %eax > + /* In parent, normal return. */ > + jnz L(no_shstk) > + > + /* NB: In child, jump back to caller via indirect branch without > + popping shadow stack which is shared with parent. Keep shadow > + stack mismatched so that child returns in the vfork-calling > + function will trigger SIGSEGV. */ > + popl %ecx > + cfi_adjust_cfa_offset (-4) > jmp *%ecx > > L(no_shstk): > - /* Jump to the return PC. Don't jump directly since this > - disturbs the branch target cache. Instead push the return > - address back on the stack. */ > - pushl %ecx > - cfi_adjust_cfa_offset (4) > #endif > > ret > diff --git a/sysdeps/unix/sysv/linux/x86/Makefile b/sysdeps/unix/sysv/linux/x86/Makefile > index 50fd018fa3..6bfd6bec49 100644 > --- a/sysdeps/unix/sysv/linux/x86/Makefile > +++ b/sysdeps/unix/sysv/linux/x86/Makefile > @@ -40,6 +40,11 @@ $(objpfx)tst-cet-property-2.out: $(objpfx)tst-cet-property-2 \ > $(evaluate-test) > endif > > +ifeq ($(subdir),posix) > +tests += tst-cet-vfork-1 > +CFLAGS-tst-cet-vfork-1.c += -mshstk > +endif > + > ifeq ($(subdir),stdlib) > tests += tst-cet-setcontext-1 > CFLAGS-tst-cet-setcontext-1.c += -mshstk > diff --git a/sysdeps/unix/sysv/linux/x86/tst-cet-vfork-1.c b/sysdeps/unix/sysv/linux/x86/tst-cet-vfork-1.c > new file mode 100644 > index 0000000000..5b9fc8c170 > --- /dev/null > +++ b/sysdeps/unix/sysv/linux/x86/tst-cet-vfork-1.c > @@ -0,0 +1,88 @@ > +/* Verify that child of the vfork-calling function can't return when > + shadow stack is in use. > + Copyright (C) 2020 Free Software Foundation, Inc. > + This file is part of the GNU C Library. > + > + The GNU C Library is free software; you can redistribute it and/or > + modify it under the terms of the GNU Lesser General Public > + License as published by the Free Software Foundation; either > + version 2.1 of the License, or (at your option) any later version. > + > + The GNU C Library is distributed in the hope that it will be useful, > + but WITHOUT ANY WARRANTY; without even the implied warranty of > + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU > + Lesser General Public License for more details. > + > + You should have received a copy of the GNU Lesser General Public > + License along with the GNU C Library; if not, see > + <https://www.gnu.org/licenses/>. */ > + > +#include <stdio.h> > +#include <stdlib.h> > +#include <unistd.h> > +#include <errno.h> > +#include <sys/types.h> > +#include <sys/wait.h> > +#include <x86intrin.h> > +#include <support/test-driver.h> > +#include <support/xsignal.h> > +#include <support/xunistd.h> > + > +__attribute__ ((noclone, noinline)) > +static void > +do_test_1 (void) > +{ > + pid_t p1; > + int fd[2]; > + > + if (pipe (fd) == -1) > + { > + puts ("pipe failed"); > + _exit (EXIT_FAILURE); > + } > + > + if ((p1 = vfork ()) == 0) > + { > + pid_t p = getpid (); > + TEMP_FAILURE_RETRY (write (fd[1], &p, sizeof (p))); > + /* Child return should trigger SIGSEGV. */ > + return; > + } > + else if (p1 == -1) > + { > + puts ("vfork failed"); > + _exit (EXIT_FAILURE); > + } > + > + pid_t p2 = 0; > + if (TEMP_FAILURE_RETRY (read (fd[0], &p2, sizeof (pid_t))) > + != sizeof (pid_t)) > + puts ("pipd read failed"); > + else > + { > + int r; > + if (TEMP_FAILURE_RETRY (waitpid (p1, &r, 0)) != p1) > + puts ("waitpid failed"); > + else if (r != 0) > + puts ("pip write in child failed"); > + } > + > + /* Parent exits immediately so that parent returns without triggering > + SIGSEGV when shadow stack isn't in use. */ > + _exit (EXIT_FAILURE); > +} > + > +static int > +do_test (void) > +{ > + /* NB: This test should trigger SIGSEGV with shadow stack enabled. */ > + if (_get_ssp () == 0) > + return EXIT_UNSUPPORTED; > + do_test_1 (); > + /* Child exits immediately so that child returns without triggering > + SIGSEGV when shadow stack isn't in use. */ > + _exit (EXIT_FAILURE); > +} > + > +#define EXPECTED_SIGNAL (_get_ssp () == 0 ? 0 : SIGSEGV) > +#include <support/test-driver.c> > diff --git a/sysdeps/unix/sysv/linux/x86_64/vfork.S b/sysdeps/unix/sysv/linux/x86_64/vfork.S > index 776d2fc610..613ff7e846 100644 > --- a/sysdeps/unix/sysv/linux/x86_64/vfork.S > +++ b/sysdeps/unix/sysv/linux/x86_64/vfork.S > @@ -20,22 +20,6 @@ > #include <bits/errno.h> > #include <tcb-offsets.h> > > -#if SHSTK_ENABLED > -/* The shadow stack prevents us from pushing the saved return PC onto > - the stack and returning normally. Instead we pop the shadow stack > - and return directly. This is the safest way to return and ensures > - any stack manipulations done by the vfork'd child doesn't cause the > - parent to terminate when CET is enabled. */ > -# undef SYSCALL_ERROR_HANDLER > -# define SYSCALL_ERROR_HANDLER \ > -0: \ > - SYSCALL_SET_ERRNO; \ > - or $-1, %RAX_LP; \ > - jmp 1b; > -# undef SYSCALL_ERROR_LABEL > -# define SYSCALL_ERROR_LABEL 0f > -#endif > - > /* Clone the calling process, but without copying the whole address space. > The calling process is suspended until the new process exits or is > replaced by a call to `execve'. Return -1 for errors, 0 to the new process, > @@ -53,17 +37,14 @@ ENTRY (__vfork) > movl $SYS_ify (vfork), %eax > syscall > > -#if !SHSTK_ENABLED > /* Push back the return PC. */ > pushq %rdi > cfi_adjust_cfa_offset(8) > -#endif > > cmpl $-4095, %eax > jae SYSCALL_ERROR_LABEL /* Branch forward if it failed. */ > > #if SHSTK_ENABLED > -1: > /* Check if shadow stack is in use. */ > xorl %esi, %esi > rdsspq %rsi > @@ -71,16 +52,19 @@ ENTRY (__vfork) > /* Normal return if shadow stack isn't in use. */ > je L(no_shstk) > > - /* Pop return address from shadow stack and jump back to caller > - directly. */ > - movl $1, %esi > - incsspq %rsi > + testl %eax, %eax > + /* In parent, normal return. */ > + jnz L(no_shstk) > + > + /* NB: In child, jump back to caller via indirect branch without > + popping shadow stack which is shared with parent. Keep shadow > + stack mismatched so that child returns in the vfork-calling > + function will trigger SIGSEGV. */ > + popq %rdi > + cfi_adjust_cfa_offset(-8) > jmp *%rdi > > L(no_shstk): > - /* Push back the return PC. */ > - pushq %rdi > - cfi_adjust_cfa_offset(8) > #endif > > /* Normal return. */ > -- > 2.26.2 >
* H. J. Lu via Libc-alpha: > Child of vfork should either call _exit or one of the exec family of > functions. But normally there is nothing to prevent child of vfork from > return of the vfork-calling function. Simpilfy x86 vfork when shadow > stack is in use to introduce mismatched shadow stack in child of vfork > to trigger SIGSEGV when the child returns from the function in which > vfork was called. Looks reasonable to me, thanks. We'll see what breaks as a result of this. 8-/ But everything that runs into crash will already have weird bugs. Thanks, Florian
diff --git a/sysdeps/unix/sysv/linux/i386/vfork.S b/sysdeps/unix/sysv/linux/i386/vfork.S index ceb41db0bd..91277a639f 100644 --- a/sysdeps/unix/sysv/linux/i386/vfork.S +++ b/sysdeps/unix/sysv/linux/i386/vfork.S @@ -21,39 +21,6 @@ #include <bits/errno.h> #include <tcb-offsets.h> -#if SHSTK_ENABLED -/* The shadow stack prevents us from pushing the saved return PC onto - the stack and returning normally. Instead we pop the shadow stack - and return directly. This is the safest way to return and ensures - any stack manipulations done by the vfork'd child doesn't cause the - parent to terminate when CET is enabled. */ -# undef SYSCALL_ERROR_HANDLER -# ifdef PIC -# define SYSCALL_ERROR_HANDLER \ -0: \ - calll .L1; \ -.L1: \ - popl %edx; \ -.L2: \ - addl $_GLOBAL_OFFSET_TABLE_ + (.L2 - .L1), %edx; \ - movl __libc_errno@gotntpoff(%edx), %edx; \ - negl %eax; \ - movl %eax, %gs:(%edx); \ - orl $-1, %eax; \ - jmp 1b; -# else -# define SYSCALL_ERROR_HANDLER \ -0: \ - movl __libc_errno@indntpoff, %edx; \ - negl %eax; \ - movl %eax, %gs:(%edx); \ - orl $-1, %eax; \ - jmp 1b; -# endif -# undef SYSCALL_ERROR_LABEL -# define SYSCALL_ERROR_LABEL 0f -#endif - /* Clone the calling process, but without copying the whole address space. The calling process is suspended until the new process exits or is replaced by a call to `execve'. Return -1 for errors, 0 to the new process, @@ -70,20 +37,17 @@ ENTRY (__vfork) movl $SYS_ify (vfork), %eax int $0x80 -#if !SHSTK_ENABLED /* Jump to the return PC. Don't jump directly since this disturbs the branch target cache. Instead push the return address back on the stack. */ pushl %ecx cfi_adjust_cfa_offset (4) -#endif cmpl $-4095, %eax /* Branch forward if it failed. */ jae SYSCALL_ERROR_LABEL #if SHSTK_ENABLED -1: /* Check if shadow stack is in use. */ xorl %edx, %edx rdsspd %edx @@ -91,18 +55,19 @@ ENTRY (__vfork) /* Normal return if shadow stack isn't in use. */ je L(no_shstk) - /* Pop return address from shadow stack and jump back to caller - directly. */ - movl $1, %edx - incsspd %edx + testl %eax, %eax + /* In parent, normal return. */ + jnz L(no_shstk) + + /* NB: In child, jump back to caller via indirect branch without + popping shadow stack which is shared with parent. Keep shadow + stack mismatched so that child returns in the vfork-calling + function will trigger SIGSEGV. */ + popl %ecx + cfi_adjust_cfa_offset (-4) jmp *%ecx L(no_shstk): - /* Jump to the return PC. Don't jump directly since this - disturbs the branch target cache. Instead push the return - address back on the stack. */ - pushl %ecx - cfi_adjust_cfa_offset (4) #endif ret diff --git a/sysdeps/unix/sysv/linux/x86/Makefile b/sysdeps/unix/sysv/linux/x86/Makefile index 50fd018fa3..6bfd6bec49 100644 --- a/sysdeps/unix/sysv/linux/x86/Makefile +++ b/sysdeps/unix/sysv/linux/x86/Makefile @@ -40,6 +40,11 @@ $(objpfx)tst-cet-property-2.out: $(objpfx)tst-cet-property-2 \ $(evaluate-test) endif +ifeq ($(subdir),posix) +tests += tst-cet-vfork-1 +CFLAGS-tst-cet-vfork-1.c += -mshstk +endif + ifeq ($(subdir),stdlib) tests += tst-cet-setcontext-1 CFLAGS-tst-cet-setcontext-1.c += -mshstk diff --git a/sysdeps/unix/sysv/linux/x86/tst-cet-vfork-1.c b/sysdeps/unix/sysv/linux/x86/tst-cet-vfork-1.c new file mode 100644 index 0000000000..5b9fc8c170 --- /dev/null +++ b/sysdeps/unix/sysv/linux/x86/tst-cet-vfork-1.c @@ -0,0 +1,88 @@ +/* Verify that child of the vfork-calling function can't return when + shadow stack is in use. + Copyright (C) 2020 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + <https://www.gnu.org/licenses/>. */ + +#include <stdio.h> +#include <stdlib.h> +#include <unistd.h> +#include <errno.h> +#include <sys/types.h> +#include <sys/wait.h> +#include <x86intrin.h> +#include <support/test-driver.h> +#include <support/xsignal.h> +#include <support/xunistd.h> + +__attribute__ ((noclone, noinline)) +static void +do_test_1 (void) +{ + pid_t p1; + int fd[2]; + + if (pipe (fd) == -1) + { + puts ("pipe failed"); + _exit (EXIT_FAILURE); + } + + if ((p1 = vfork ()) == 0) + { + pid_t p = getpid (); + TEMP_FAILURE_RETRY (write (fd[1], &p, sizeof (p))); + /* Child return should trigger SIGSEGV. */ + return; + } + else if (p1 == -1) + { + puts ("vfork failed"); + _exit (EXIT_FAILURE); + } + + pid_t p2 = 0; + if (TEMP_FAILURE_RETRY (read (fd[0], &p2, sizeof (pid_t))) + != sizeof (pid_t)) + puts ("pipd read failed"); + else + { + int r; + if (TEMP_FAILURE_RETRY (waitpid (p1, &r, 0)) != p1) + puts ("waitpid failed"); + else if (r != 0) + puts ("pip write in child failed"); + } + + /* Parent exits immediately so that parent returns without triggering + SIGSEGV when shadow stack isn't in use. */ + _exit (EXIT_FAILURE); +} + +static int +do_test (void) +{ + /* NB: This test should trigger SIGSEGV with shadow stack enabled. */ + if (_get_ssp () == 0) + return EXIT_UNSUPPORTED; + do_test_1 (); + /* Child exits immediately so that child returns without triggering + SIGSEGV when shadow stack isn't in use. */ + _exit (EXIT_FAILURE); +} + +#define EXPECTED_SIGNAL (_get_ssp () == 0 ? 0 : SIGSEGV) +#include <support/test-driver.c> diff --git a/sysdeps/unix/sysv/linux/x86_64/vfork.S b/sysdeps/unix/sysv/linux/x86_64/vfork.S index 776d2fc610..613ff7e846 100644 --- a/sysdeps/unix/sysv/linux/x86_64/vfork.S +++ b/sysdeps/unix/sysv/linux/x86_64/vfork.S @@ -20,22 +20,6 @@ #include <bits/errno.h> #include <tcb-offsets.h> -#if SHSTK_ENABLED -/* The shadow stack prevents us from pushing the saved return PC onto - the stack and returning normally. Instead we pop the shadow stack - and return directly. This is the safest way to return and ensures - any stack manipulations done by the vfork'd child doesn't cause the - parent to terminate when CET is enabled. */ -# undef SYSCALL_ERROR_HANDLER -# define SYSCALL_ERROR_HANDLER \ -0: \ - SYSCALL_SET_ERRNO; \ - or $-1, %RAX_LP; \ - jmp 1b; -# undef SYSCALL_ERROR_LABEL -# define SYSCALL_ERROR_LABEL 0f -#endif - /* Clone the calling process, but without copying the whole address space. The calling process is suspended until the new process exits or is replaced by a call to `execve'. Return -1 for errors, 0 to the new process, @@ -53,17 +37,14 @@ ENTRY (__vfork) movl $SYS_ify (vfork), %eax syscall -#if !SHSTK_ENABLED /* Push back the return PC. */ pushq %rdi cfi_adjust_cfa_offset(8) -#endif cmpl $-4095, %eax jae SYSCALL_ERROR_LABEL /* Branch forward if it failed. */ #if SHSTK_ENABLED -1: /* Check if shadow stack is in use. */ xorl %esi, %esi rdsspq %rsi @@ -71,16 +52,19 @@ ENTRY (__vfork) /* Normal return if shadow stack isn't in use. */ je L(no_shstk) - /* Pop return address from shadow stack and jump back to caller - directly. */ - movl $1, %esi - incsspq %rsi + testl %eax, %eax + /* In parent, normal return. */ + jnz L(no_shstk) + + /* NB: In child, jump back to caller via indirect branch without + popping shadow stack which is shared with parent. Keep shadow + stack mismatched so that child returns in the vfork-calling + function will trigger SIGSEGV. */ + popq %rdi + cfi_adjust_cfa_offset(-8) jmp *%rdi L(no_shstk): - /* Push back the return PC. */ - pushq %rdi - cfi_adjust_cfa_offset(8) #endif /* Normal return. */