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selftests/x86/ldt_gdt: Robustify against set_thread_area() and LAR oddities

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Bits 19:16 of LAR's result are undefined, and some upcoming
improvements to the test case seem to trigger this.  Mask off those
bits to avoid spurious failures.

commit 5b781c7e31 ("x86/tls: Forcibly set the accessed bit in TLS
segments") adds a valid case in which LAR's output doesn't quite
agree with set_thread_area()'s input.  This isn't triggered in the
test as is, but it will be if we start calling set_thread_area()
with the accessed bit clear.  Work around this discrepency.

I've added a Fixes tag so that -stable can pick this up if neccesary.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 5b781c7e31 ("x86/tls: Forcibly set the accessed bit in TLS segments")
Link: http://lkml.kernel.org/r/b82f3f89c034b53580970ac865139fd8863f44e2.1509794321.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Andy Lutomirski 2017-11-04 04:19:49 -07:00 committed by Ingo Molnar
parent 693cb5580f
commit d60ad744c9
1 changed files with 9 additions and 1 deletions
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10
tools/testing/selftests/x86/ldt_gdt.c
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@ -115,7 +115,15 @@ static void check_valid_segment(uint16_t index, int ldt,
return;
}
if (ar != expected_ar) {
/* The SDM says "bits 19:16 are undefined". Thanks. */
ar &= ~0xF0000;
/*
* NB: Different Linux versions do different things with the
* accessed bit in set_thread_area().
*/
if (ar != expected_ar &&
(ldt || ar != (expected_ar | AR_ACCESSED))) {
printf("[FAIL]\t%s entry %hu has AR 0x%08X but expected 0x%08X\n",
(ldt ? "LDT" : "GDT"), index, ar, expected_ar);
nerrs++;