Messages in this thread Patch in this message | | | Date | Sat, 27 Oct 2007 14:08:37 -0400 | From | Mathieu Desnoyers <> | Subject | [PATCH] Fix x86_64 TIF_SYSCALL_TRACE race in entry.S |
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Fix x86_64 TIF_SYSCALL_TRACE race in entry.S
When the flag is inactive upon syscall entry and concurrently activated before exit, we seem to reach a state where the top of stack is incorrect upon return to user space.
Fix this by fixing the top of stack and jumping to int_ret_from_sys_call if we detect that thread flags has been modified.
We make sure that the thread flag read is coherent between our new test and the ALLWORK_MASK test by first saving it in a register used for both comparisons.
It applies on top of 2.6.23-mm1 or 2.6.23.1. If you think the implementation is correct, I'll port it to 2.6.24-rc1.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> CC: Andi Kleen <ak@muc.de> --- arch/x86_64/kernel/entry.S | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)
Index: linux-2.6-lttng/arch/x86_64/kernel/entry.S =================================================================== --- linux-2.6-lttng.orig/arch/x86_64/kernel/entry.S 2007-10-27 14:01:12.000000000 -0400 +++ linux-2.6-lttng/arch/x86_64/kernel/entry.S 2007-10-27 14:01:28.000000000 -0400 @@ -245,9 +245,11 @@ ret_from_sys_call: /* edi: flagmask */ sysret_check: GET_THREAD_INFO(%rcx) + movl threadinfo_flags(%rcx),%edx + testl $(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SECCOMP),%edx + jnz ret_from_sys_call_trace cli TRACE_IRQS_OFF - movl threadinfo_flags(%rcx),%edx andl %edi,%edx jnz sysret_careful CFI_REMEMBER_STATE @@ -278,6 +280,14 @@ sysret_careful: CFI_ADJUST_CFA_OFFSET -8 jmp sysret_check +ret_from_sys_call_trace: + SAVE_REST + FIXUP_TOP_OF_STACK %rdi + movq %rsp,%rdi + LOAD_ARGS ARGOFFSET /* reload args from stack in case ptrace changed it */ + RESTORE_REST + jmp int_ret_from_sys_call + /* Handle a signal */ sysret_signal: TRACE_IRQS_ON -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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