Commit 26c2d2b3 authored Oct 23, 2014 by Eric Paris Committed by H. Peter Anvin Oct 24, 2014

i386/audit: stop scribbling on the stack frame

git commit b4f0d375 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>

parent db65bcfd

arch/x86/kernel/entry_32.S

+7 −8

Original line number	Diff line number	Diff line
		@@ -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