| Message ID | 1333051320-30872-14-git-send-email-wad@chromium.org |
|---|---|
| State | Not Applicable, archived |
| Delegated to: | David Miller |
| Headers | show |
On Thu, 29 Mar 2012 15:01:58 -0500 Will Drewry <wad@chromium.org> wrote: > This change adds support for a new ptrace option, PTRACE_O_TRACESECCOMP, > and a new return value for seccomp BPF programs, SECCOMP_RET_TRACE. > > When a tracer specifies the PTRACE_O_TRACESECCOMP ptrace option, the > tracer will be notified, via PTRACE_EVENT_SECCOMP, for any syscall that > results in a BPF program returning SECCOMP_RET_TRACE. The 16-bit > SECCOMP_RET_DATA mask of the BPF program return value will be passed as > the ptrace_message and may be retrieved using PTRACE_GETEVENTMSG. > > If the subordinate process is not using seccomp filter, then no > system call notifications will occur even if the option is specified. > > If there is no tracer with PTRACE_O_TRACESECCOMP when SECCOMP_RET_TRACE > is returned, the system call will not be executed and an -ENOSYS errno > will be returned to userspace. > > This change adds a dependency on the system call slow path. Any future > efforts to use the system call fast path for seccomp filter will need to > address this restriction. > > > ... > > @@ -410,6 +411,15 @@ int __secure_computing_int(int this_syscall) > /* Let the filter pass back 16 bits of data. */ > seccomp_send_sigsys(this_syscall, data); > goto skip; > + case SECCOMP_RET_TRACE: > + /* Skip these calls if there is no tracer. */ > + if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) > + goto skip; > + /* Allow the BPF to provide the event message */ > + ptrace_event(PTRACE_EVENT_SECCOMP, data); > + if (fatal_signal_pending(current)) > + break; I don't have all the patches applied here so the context is missing. Perhaps tht would help me understand what this fatal_signal_pending() test is doing here. But an explanatory comment wouldn't hurt. What *is* it here for, anyway? > + return 0; > case SECCOMP_RET_ALLOW: > return 0; > case SECCOMP_RET_KILL: -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, Apr 6, 2012 at 4:24 PM, Andrew Morton <akpm@linux-foundation.org> wrote: > On Thu, 29 Mar 2012 15:01:58 -0500 > Will Drewry <wad@chromium.org> wrote: > >> This change adds support for a new ptrace option, PTRACE_O_TRACESECCOMP, >> and a new return value for seccomp BPF programs, SECCOMP_RET_TRACE. >> >> When a tracer specifies the PTRACE_O_TRACESECCOMP ptrace option, the >> tracer will be notified, via PTRACE_EVENT_SECCOMP, for any syscall that >> results in a BPF program returning SECCOMP_RET_TRACE. The 16-bit >> SECCOMP_RET_DATA mask of the BPF program return value will be passed as >> the ptrace_message and may be retrieved using PTRACE_GETEVENTMSG. >> >> If the subordinate process is not using seccomp filter, then no >> system call notifications will occur even if the option is specified. >> >> If there is no tracer with PTRACE_O_TRACESECCOMP when SECCOMP_RET_TRACE >> is returned, the system call will not be executed and an -ENOSYS errno >> will be returned to userspace. >> >> This change adds a dependency on the system call slow path. Any future >> efforts to use the system call fast path for seccomp filter will need to >> address this restriction. >> >> >> ... >> >> @@ -410,6 +411,15 @@ int __secure_computing_int(int this_syscall) >> /* Let the filter pass back 16 bits of data. */ >> seccomp_send_sigsys(this_syscall, data); >> goto skip; >> + case SECCOMP_RET_TRACE: >> + /* Skip these calls if there is no tracer. */ >> + if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) >> + goto skip; >> + /* Allow the BPF to provide the event message */ >> + ptrace_event(PTRACE_EVENT_SECCOMP, data); >> + if (fatal_signal_pending(current)) >> + break; > > I don't have all the patches applied here so the context is missing. > Perhaps tht would help me understand what this fatal_signal_pending() > test is doing here. But an explanatory comment wouldn't hurt. I'll add a comment along the lines of my answer below! > What *is* it here for, anyway? The timely delivery of a fatal signal will silently block tracer event notification. By immediately terminating if a fatal signal is pending, we avoid accidentally executing a system call that the tracer did not approve of. http://lxr.linux.no/linux+v3.3.1/kernel/signal.c#L1839 I can be more verbose, but hopefully that covers it well enough - thanks! -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/arch/Kconfig b/arch/Kconfig index a24d213..fafefe6 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -216,15 +216,16 @@ config HAVE_CMPXCHG_DOUBLE config HAVE_ARCH_SECCOMP_FILTER bool help - This symbol should be selected by an architecure if it provides: - asm/syscall.h: + An arch should select this symbol if it provides all of these things: - syscall_get_arch() - syscall_get_arguments() - syscall_rollback() - syscall_set_return_value() - SIGSYS siginfo_t support must be implemented. - __secure_computing_int()/secure_computing()'s return value must be - checked, with -1 resulting in the syscall being skipped. + - SIGSYS siginfo_t support + - uses __secure_computing_int() or secure_computing() + - secure_computing is called from a ptrace_event()-safe context + - secure_computing return value is checked and a return value of -1 + results in the system call being skipped immediately. config SECCOMP_FILTER def_bool y diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h index 5c71962..597e4fd 100644 --- a/include/linux/ptrace.h +++ b/include/linux/ptrace.h @@ -58,6 +58,7 @@ #define PTRACE_EVENT_EXEC 4 #define PTRACE_EVENT_VFORK_DONE 5 #define PTRACE_EVENT_EXIT 6 +#define PTRACE_EVENT_SECCOMP 7 /* Extended result codes which enabled by means other than options. */ #define PTRACE_EVENT_STOP 128 @@ -69,8 +70,9 @@ #define PTRACE_O_TRACEEXEC (1 << PTRACE_EVENT_EXEC) #define PTRACE_O_TRACEVFORKDONE (1 << PTRACE_EVENT_VFORK_DONE) #define PTRACE_O_TRACEEXIT (1 << PTRACE_EVENT_EXIT) +#define PTRACE_O_TRACESECCOMP (1 << PTRACE_EVENT_SECCOMP) -#define PTRACE_O_MASK 0x0000007f +#define PTRACE_O_MASK 0x000000ff #include <asm/ptrace.h> @@ -98,6 +100,7 @@ #define PT_TRACE_EXEC PT_EVENT_FLAG(PTRACE_EVENT_EXEC) #define PT_TRACE_VFORK_DONE PT_EVENT_FLAG(PTRACE_EVENT_VFORK_DONE) #define PT_TRACE_EXIT PT_EVENT_FLAG(PTRACE_EVENT_EXIT) +#define PT_TRACE_SECCOMP PT_EVENT_FLAG(PTRACE_EVENT_SECCOMP) /* single stepping state bits (used on ARM and PA-RISC) */ #define PT_SINGLESTEP_BIT 31 diff --git a/include/linux/seccomp.h b/include/linux/seccomp.h index ecec06c..41ff13b 100644 --- a/include/linux/seccomp.h +++ b/include/linux/seccomp.h @@ -21,6 +21,7 @@ #define SECCOMP_RET_KILL 0x00000000U /* kill the task immediately */ #define SECCOMP_RET_TRAP 0x00030000U /* disallow and force a SIGSYS */ #define SECCOMP_RET_ERRNO 0x00050000U /* returns an errno */ +#define SECCOMP_RET_TRACE 0x7ff00000U /* pass to a tracer or disallow */ #define SECCOMP_RET_ALLOW 0x7fff0000U /* allow */ /* Masks for the return value sections. */ diff --git a/kernel/seccomp.c b/kernel/seccomp.c index 9a59c93..4b5affa 100644 --- a/kernel/seccomp.c +++ b/kernel/seccomp.c @@ -24,6 +24,7 @@ #ifdef CONFIG_SECCOMP_FILTER #include <asm/syscall.h> #include <linux/filter.h> +#include <linux/ptrace.h> #include <linux/security.h> #include <linux/slab.h> #include <linux/tracehook.h> @@ -398,7 +399,7 @@ int __secure_computing_int(int this_syscall) case SECCOMP_MODE_FILTER: ret = seccomp_run_filters(this_syscall); data = ret & SECCOMP_RET_DATA; - switch (code & SECCOMP_RET_ACTION) { + switch (ret & SECCOMP_RET_ACTION) { case SECCOMP_RET_ERRNO: /* Set the low-order 16-bits as a errno. */ syscall_set_return_value(current, task_pt_regs(current), @@ -410,6 +411,15 @@ int __secure_computing_int(int this_syscall) /* Let the filter pass back 16 bits of data. */ seccomp_send_sigsys(this_syscall, data); goto skip; + case SECCOMP_RET_TRACE: + /* Skip these calls if there is no tracer. */ + if (!ptrace_event_enabled(current, PTRACE_EVENT_SECCOMP)) + goto skip; + /* Allow the BPF to provide the event message */ + ptrace_event(PTRACE_EVENT_SECCOMP, data); + if (fatal_signal_pending(current)) + break; + return 0; case SECCOMP_RET_ALLOW: return 0; case SECCOMP_RET_KILL:
This change adds support for a new ptrace option, PTRACE_O_TRACESECCOMP, and a new return value for seccomp BPF programs, SECCOMP_RET_TRACE. When a tracer specifies the PTRACE_O_TRACESECCOMP ptrace option, the tracer will be notified, via PTRACE_EVENT_SECCOMP, for any syscall that results in a BPF program returning SECCOMP_RET_TRACE. The 16-bit SECCOMP_RET_DATA mask of the BPF program return value will be passed as the ptrace_message and may be retrieved using PTRACE_GETEVENTMSG. If the subordinate process is not using seccomp filter, then no system call notifications will occur even if the option is specified. If there is no tracer with PTRACE_O_TRACESECCOMP when SECCOMP_RET_TRACE is returned, the system call will not be executed and an -ENOSYS errno will be returned to userspace. This change adds a dependency on the system call slow path. Any future efforts to use the system call fast path for seccomp filter will need to address this restriction. v17: - rebase onto refactored ptrace code now in -linus v16: - update PT_TRACE_MASK to 0xbf4 so that STOP isn't clear on SETOPTIONS call (indan@nul.nu) [note PT_TRACE_MASK disappears in linux-next] v15: - add audit support for non-zero return codes - clean up style (indan@nul.nu) v14: - rebase/nochanges v13: - rebase on to 88ebdda6159ffc15699f204c33feb3e431bf9bdc (Brings back a change to ptrace.c and the masks.) v12: - rebase to linux-next - use ptrace_event and update arch/Kconfig to mention slow-path dependency - drop all tracehook changes and inclusion (oleg@redhat.com) v11: - invert the logic to just make it a PTRACE_SYSCALL accelerator (indan@nul.nu) v10: - moved to PTRACE_O_SECCOMP / PT_TRACE_SECCOMP v9: - n/a v8: - guarded PTRACE_SECCOMP use with an ifdef v7: - introduced Signed-off-by: Will Drewry <wad@chromium.org> --- arch/Kconfig | 11 ++++++----- include/linux/ptrace.h | 5 ++++- include/linux/seccomp.h | 1 + kernel/seccomp.c | 12 +++++++++++- 4 files changed, 22 insertions(+), 7 deletions(-)