Re: [PATCH] i386/audit: stop scribbling on the stack frame

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 using the values still in those registers. 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(a)gmail.com&gt; Signed-off-by: Eric Paris <eparis(a)redhat.com&gt; Signed-off-by: Richard Guy Briggs <rgb(a)redhat.com&gt; Cc: Thomas Gleixner <tglx(a)linutronix.de&gt; Cc: Ingo Molnar <mingo(a)redhat.com&gt; Cc: "H. Peter Anvin" <hpa(a)zytor.com&gt; Cc: x86(a)kernel.org Cc: linux-kernel(a)vger.kernel.org Cc: linux-audit(a)redhat.com --- On 14/10/25, Thomas Gleixner wrote: > Why are we grabbing that from the stack? AFAICT all arguments are in > the registers still. Right, re-arranging the instructions slightly to avoid overwriting %edx with %ebx before needing it to push onto the stack, how does this look? 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 b553ed8..344b63f 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_ECX(%esp), %ecx already set, a1: 3nd arg to audit */ + /* movl PT_EAX(%esp), %eax already set, syscall number: 1st arg to audit */ + pushl_cfi %esi /* a3: 5th arg */ + pushl_cfi %edx /* a2: 4th arg */ + movl %ebx, %edx /* ebx/a0: 2nd arg to audit */ 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 - RGB -- Richard Guy Briggs <rbriggs(a)redhat.com&gt; Senior Software Engineer, Kernel Security, AMER ENG Base Operating Systems, Red Hat Remote, Ottawa, Canada Voice: +1.647.777.2635, Internal: (81) 32635, Alt: +1.613.693.0684x3545