summaryrefslogtreecommitdiffstats
diff options
context:
space:
mode:
authorAndy Lutomirski <luto@kernel.org>2017-11-22 20:39:16 -0800
committerIngo Molnar <mingo@kernel.org>2017-11-23 07:54:25 +0100
commitca37e57bbe0cf1455ea3e84eb89ed04a132d59e1 (patch)
tree551fedc84398952e421dbe51919e29e4c03fc49f
parentf68d62a56708b0c19dca7a998f408510f2fbc3a8 (diff)
x86/entry/64: Add missing irqflags tracing to native_load_gs_index()
Running this code with IRQs enabled (where dummy_lock is a spinlock): static void check_load_gs_index(void) { /* This will fail. */ load_gs_index(0xffff); spin_lock(&dummy_lock); spin_unlock(&dummy_lock); } Will generate a lockdep warning. The issue is that the actual write to %gs would cause an exception with IRQs disabled, and the exception handler would, as an inadvertent side effect, update irqflag tracing to reflect the IRQs-off status. native_load_gs_index() would then turn IRQs back on and return with irqflag tracing still thinking that IRQs were off. The dummy lock-and-unlock causes lockdep to notice the error and warn. Fix it by adding the missing tracing. Apparently nothing did this in a context where it mattered. I haven't tried to find a code path that would actually exhibit the warning if appropriately nasty user code were running. I suspect that the security impact of this bug is very, very low -- production systems don't run with lockdep enabled, and the warning is mostly harmless anyway. Found during a quick audit of the entry code to try to track down an unrelated bug that Ingo found in some still-in-development code. Signed-off-by: Andy Lutomirski <luto@kernel.org> Cc: Borislav Petkov <bpetkov@suse.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/e1aeb0e6ba8dd430ec36c8a35e63b429698b4132.1511411918.git.luto@kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
-rw-r--r--arch/x86/entry/entry_64.S10
1 files changed, 8 insertions, 2 deletions
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 5063ed1214dd..f81d50d7ceac 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -51,15 +51,19 @@ ENTRY(native_usergs_sysret64)
END(native_usergs_sysret64)
#endif /* CONFIG_PARAVIRT */
-.macro TRACE_IRQS_IRETQ
+.macro TRACE_IRQS_FLAGS flags:req
#ifdef CONFIG_TRACE_IRQFLAGS
- bt $9, EFLAGS(%rsp) /* interrupts off? */
+ bt $9, \flags /* interrupts off? */
jnc 1f
TRACE_IRQS_ON
1:
#endif
.endm
+.macro TRACE_IRQS_IRETQ
+ TRACE_IRQS_FLAGS EFLAGS(%rsp)
+.endm
+
/*
* When dynamic function tracer is enabled it will add a breakpoint
* to all locations that it is about to modify, sync CPUs, update
@@ -943,11 +947,13 @@ ENTRY(native_load_gs_index)
FRAME_BEGIN
pushfq
DISABLE_INTERRUPTS(CLBR_ANY & ~CLBR_RDI)
+ TRACE_IRQS_OFF
SWAPGS
.Lgs_change:
movl %edi, %gs
2: ALTERNATIVE "", "mfence", X86_BUG_SWAPGS_FENCE
SWAPGS
+ TRACE_IRQS_FLAGS (%rsp)
popfq
FRAME_END
ret