| From | alexander.levin@verizon ... | Subject | [PATCH AUTOSEL for 4.14 06/51] selftests/x86/ldt_gdt: Robustify against set_thread_area() and LAR oddities | Date | Wed, 22 Nov 2017 22:25:37 +0000 |
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From: Andy Lutomirski <luto@kernel.org>
[ Upstream commit d60ad744c9741586010d4bea286f09a063a90fbd ]
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 5b781c7e317f ("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: 5b781c7e317f ("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> Signed-off-by: Sasha Levin <alexander.levin@verizon.com> --- tools/testing/selftests/x86/ldt_gdt.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/tools/testing/selftests/x86/ldt_gdt.c b/tools/testing/selftests/x86/ldt_gdt.c index b1779da72428..2afc41a3730f 100644 --- a/tools/testing/selftests/x86/ldt_gdt.c +++ b/tools/testing/selftests/x86/ldt_gdt.c @@ -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++; -- 2.11.0
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