Well, probably not something for stable/urgent... On October 23, 2014 11:39:48 AM PDT, Andy Lutomirski <l...@amacapital.net> wrote: >On 10/22/2014 09:04 PM, Eric Paris wrote: >> git commit b4f0d3755c5e9cc86292d5fd78261903b4f23d4a was very very >dumb. >> It was writing over %esp/pt_regs semi-randomly on i686 with the >expected >> "system can't boot" results. As noted in: >> >> https://bugs.freedesktop.org/show_bug.cgi?id=85277 >> >> This patch stops fscking with pt_regs. Instead it sets up the >registers >> for the call to __audit_syscall_entry in the most obvious conceivable >> way. It then does just a tiny tiny touch of magic. We need to get >what >> started in PT_EDX into 0(%esp) and PT_ESI into 4(%esp). This is as >easy >> as a pair of pushes. >> >> After the call to __audit_syscall_entry all we need to do is get that >> now useless junk off the stack (pair of pops) and reload %eax with >the >> original syscall so other stuff can keep going about it's business. >> >> Signed-off-by: Eric Paris <epa...@redhat.com> >> Cc: Thomas Gleixner <t...@linutronix.de> >> Cc: Ingo Molnar <mi...@redhat.com> >> Cc: "H. Peter Anvin" <h...@zytor.com> >> Cc: x...@kernel.org >> Cc: linux-kernel@vger.kernel.org >> Cc: linux-au...@redhat.com >> --- >> arch/x86/kernel/entry_32.S | 15 +++++++-------- >> 1 file changed, 7 insertions(+), 8 deletions(-) >> >> diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S >> index f9e3fab..fb01d22 100644 >> --- a/arch/x86/kernel/entry_32.S >> +++ b/arch/x86/kernel/entry_32.S >> @@ -447,15 +447,14 @@ sysenter_exit: >> sysenter_audit: >> testl $(_TIF_WORK_SYSCALL_ENTRY & >~_TIF_SYSCALL_AUDIT),TI_flags(%ebp) >> jnz syscall_trace_entry >> - addl $4,%esp >> - CFI_ADJUST_CFA_OFFSET -4 >> - movl %esi,4(%esp) /* 5th arg: 4th syscall arg */ >> - movl %edx,(%esp) /* 4th arg: 3rd syscall arg */ >> - /* %ecx already in %ecx 3rd arg: 2nd syscall arg */ >> - movl %ebx,%edx /* 2nd arg: 1st syscall arg */ >> - /* %eax already in %eax 1st arg: syscall number */ >> + /* movl PT_EAX(%esp), %eax already set, syscall number: 1st arg to >audit */ >> + movl PT_EBX(%esp), %edx /* ebx/a0: 2nd arg to audit */ >> + /* movl PT_ECX(%esp), %ecx already set, a1: 3nd arg to audit */ >> + pushl_cfi PT_ESI(%esp) /* a3: 5th arg */ >> + pushl_cfi PT_EDX+4(%esp) /* a2: 4th arg */ >> call __audit_syscall_entry >> - pushl_cfi %ebx >> + popl_cfi %ecx /* get that remapped edx off the stack */ >> + popl_cfi %ecx /* get that remapped esi off the stack */ >> movl PT_EAX(%esp),%eax /* reload syscall number */ >> jmp sysenter_do_call >> >> > >This looks reasonably likely to be correct, but this code is >complicated >and now ever slower. > >How hard would it be to just delete it and replace it with a >straightforward two-phase trace invocation a la x86_64? > >--Andy
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