Commit c2c9b52f authored Mar 09, 2016 by Andy Lutomirski Committed by Ingo Molnar Mar 10, 2016

x86/entry/32: Restore FLAGS on SYSEXIT



We weren't restoring FLAGS at all on SYSEXIT.  Apparently no one cared.

With this patch applied, native kernels should always honor
task_pt_regs()->flags, which opens the door for some sys_iopl()
cleanups.  I'll do those as a separate series, though, since getting
it right will involve tweaking some paravirt ops.

( The short version is that, before this patch, sys_iopl(), invoked via
  SYSENTER, wasn't guaranteed to ever transfer the updated
  regs->flags, so sys_iopl() had to change the hardware flags register
  as well. )

Reported-by: Brian Gerst <brgerst@gmail.com>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/3f98b207472dc9784838eb5ca2b89dcc845ce269.1457578375.git.luto@kernel.org


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 67f590e8

arch/x86/entry/entry_32.S

+9 −0

Original line number	Diff line number	Diff line
		@@ -342,6 +342,15 @@ sysenter_past_esp:
		popl %ebp /* pt_regs->bp */
		popl %eax /* pt_regs->ax */

		/*
		* Restore all flags except IF. (We restore IF separately because
		* STI gives a one-instruction window in which we won't be interrupted,
		* whereas POPF does not.)
		*/
		addl $PT_EFLAGS-PT_DS, %esp /* point esp at pt_regs->flags */
		btr $X86_EFLAGS_IF_BIT, (%esp)
		popfl

		/*
		* Return back to the vDSO, which will pop ecx and edx.
		* Don't bother with DS and ES (they already contain __USER_DS).