x86/nmi: CVE-2015-3290 fixes
This is the first three patches in the NMI series. They fix
CVE-2015-3290. I omitted the fix for CVE-2015-3291 and the testing
patches because they're far less urgent.
x86/nmi/64: Switch stacks on userspace NMI entry
Returning to userspace is tricky: IRET can fail, and ESPFIX can
rearrange the stack prior to IRET.
The NMI nesting fixup relies on a precise stack layout and atomic
IRET. Rather than trying to teach the NMI nesting fixup to handle
ESPFIX and failed IRET, punt: run NMIs that came from user mode on
the normal kernel stack.
This will make some nested NMIs visible to C code, but the C code is
okay with that.
As a side effect, this should speed up perf: it eliminates an RDMSR
when NMIs come from user mode.
Fixes CVE-2015-3290.
Cc: stable@vger.kernel.org
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Reviewed-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
1 file changed
