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linux/arch/x86/entry
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Andy Lutomirski f9a64e23a9 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>
History 2017-11-30 08:40:39 +00:00
..
syscalls License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
vdso License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
vsyscall License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
calling.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
common.c x86/syscalls: Check address limit on user-mode return 2017-07-08 14:05:32 +02:00
entry_32.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
entry_64.S x86/entry/64: Add missing irqflags tracing to native_load_gs_index() 2017-11-30 08:40:39 +00:00
entry_64_compat.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
Makefile License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
syscall_32.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
syscall_64.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
thunk_32.S x86: move exports to actual definitions 2016-08-07 23:47:15 -04:00
thunk_64.S x86: move exports to actual definitions 2016-08-07 23:47:15 -04:00