x86/entry/64: Add missing irqflags tracing to native_load_gs_index()
commit ca37e57bbe
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>
This commit is contained in:
Родитель
c91f3fc241
Коммит
f9a64e23a9
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@ -51,15 +51,19 @@ ENTRY(native_usergs_sysret64)
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END(native_usergs_sysret64)
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#endif /* CONFIG_PARAVIRT */
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.macro TRACE_IRQS_IRETQ
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.macro TRACE_IRQS_FLAGS flags:req
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#ifdef CONFIG_TRACE_IRQFLAGS
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bt $9, EFLAGS(%rsp) /* interrupts off? */
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bt $9, \flags /* interrupts off? */
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jnc 1f
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TRACE_IRQS_ON
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1:
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#endif
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.endm
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.macro TRACE_IRQS_IRETQ
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TRACE_IRQS_FLAGS EFLAGS(%rsp)
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.endm
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/*
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* When dynamic function tracer is enabled it will add a breakpoint
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* to all locations that it is about to modify, sync CPUs, update
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@ -923,11 +927,13 @@ ENTRY(native_load_gs_index)
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FRAME_BEGIN
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pushfq
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DISABLE_INTERRUPTS(CLBR_ANY & ~CLBR_RDI)
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TRACE_IRQS_OFF
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SWAPGS
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.Lgs_change:
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movl %edi, %gs
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2: ALTERNATIVE "", "mfence", X86_BUG_SWAPGS_FENCE
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SWAPGS
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TRACE_IRQS_FLAGS (%rsp)
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popfq
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FRAME_END
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ret
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