diff options
author | Andy Lutomirski <luto@kernel.org> | 2017-11-22 20:39:16 -0800 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2017-11-30 08:39:01 +0000 |
commit | 0d794d0d018f23fb09c50f6ae26868bd6ae343d6 (patch) | |
tree | 2e2498a8409f47cd0db4bff54efc1516c1fa3207 /arch | |
parent | 2816c0455cea088f07a210f8a00701a82a78aa9c (diff) |
x86/entry/64: Add missing irqflags tracing to native_load_gs_index()
commit ca37e57bbe0cf1455ea3e84eb89ed04a132d59e1 upstream.
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>
Link: http://lkml.kernel.org/r/e1aeb0e6ba8dd430ec36c8a35e63b429698b4132.1511411918.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'arch')
-rw-r--r-- | arch/x86/entry/entry_64.S | 10 |
1 files changed, 8 insertions, 2 deletions
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index e7b0e7ff4c58..be9df513141e 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -54,15 +54,19 @@ ENTRY(native_usergs_sysret64) ENDPROC(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 @@ -868,11 +872,13 @@ idtentry simd_coprocessor_error do_simd_coprocessor_error has_error_code=0 ENTRY(native_load_gs_index) 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 ret END(native_load_gs_index) |