diff options
| author | Steven Rostedt | 2012-06-07 11:54:37 -0400 |
|---|---|---|
| committer | Steven Rostedt | 2012-06-08 18:51:12 -0400 |
| commit | 70fb74a5420f9caa3e001d65004e4b669124283e (patch) | |
| tree | a099c86b2e63dc5d6246b8efe07a5b3e91b1301e /arch/x86/kernel/nmi.c | |
| parent | c7d65a78fc18ed70353baeb7497ec71a7c775ac5 (diff) | |
x86: Save cr2 in NMI in case NMIs take a page fault (for i386)
Avi Kivity reported that page faults in NMIs could cause havic if
the NMI preempted another page fault handler:
The recent changes to NMI allow exceptions to take place in NMI
handlers, but I think that a #PF (say, due to access to vmalloc space)
is still problematic. Consider the sequence
#PF (cr2 set by processor)
NMI
...
#PF (cr2 clobbered)
do_page_fault()
IRET
...
IRET
do_page_fault()
address = read_cr2()
The last line reads the overwritten cr2 value.
This is the i386 version, which has the luxury of doing the work
in C code.
Link: http://lkml.kernel.org/r/4FBB8C40.6080304@redhat.com
Reported-by: Avi Kivity <avi@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'arch/x86/kernel/nmi.c')
| -rw-r--r-- | arch/x86/kernel/nmi.c | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c index a15a88800661..f84f5c57de35 100644 --- a/arch/x86/kernel/nmi.c +++ b/arch/x86/kernel/nmi.c @@ -395,6 +395,14 @@ static __kprobes void default_do_nmi(struct pt_regs *regs) * thus there is no race between the first check of state for NOT_RUNNING * and setting it to NMI_EXECUTING. The HW will prevent nested NMIs * at this point. + * + * In case the NMI takes a page fault, we need to save off the CR2 + * because the NMI could have preempted another page fault and corrupt + * the CR2 that is about to be read. As nested NMIs must be restarted + * and they can not take breakpoints or page faults, the update of the + * CR2 must be done before converting the nmi state back to NOT_RUNNING. + * Otherwise, there would be a race of another nested NMI coming in + * after setting state to NOT_RUNNING but before updating the nmi_cr2. */ enum nmi_states { NMI_NOT_RUNNING = 0, @@ -402,6 +410,7 @@ enum nmi_states { NMI_LATCHED, }; static DEFINE_PER_CPU(enum nmi_states, nmi_state); +static DEFINE_PER_CPU(unsigned long, nmi_cr2); #define nmi_nesting_preprocess(regs) \ do { \ @@ -410,11 +419,14 @@ static DEFINE_PER_CPU(enum nmi_states, nmi_state); return; \ } \ this_cpu_write(nmi_state, NMI_EXECUTING); \ + this_cpu_write(nmi_cr2, read_cr2()); \ } while (0); \ nmi_restart: #define nmi_nesting_postprocess() \ do { \ + if (unlikely(this_cpu_read(nmi_cr2) != read_cr2())) \ + write_cr2(this_cpu_read(nmi_cr2)); \ if (this_cpu_dec_return(nmi_state)) \ goto nmi_restart; \ } while (0) |