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i386/audit: stop scribbling on the stack frame

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git commit b4f0d3755c 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.

Reported-by: Paulo Zanoni <przanoni@gmail.com>
Signed-off-by: Eric Paris <eparis@redhat.com>
Link: http://lkml.kernel.org/r/1414037043-30647-1-git-send-email-eparis@redhat.com
Cc: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
Eric Paris 2014-10-23 00:04:03 -04:00 committed by H. Peter Anvin
parent db65bcfd95
commit 26c2d2b391
1 changed files with 7 additions and 8 deletions
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15
arch/x86/kernel/entry_32.S
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@ -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