Commit-ID: d60ad744c9741586010d4bea286f09a063a90fbd
Gitweb: https://git.kernel.org/tip/d60ad744c9741586010d4bea286f09a063a90fbd
Author: Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate: Sat, 4 Nov 2017 04:19:49 -0700
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 7 Nov 2017 11:13:42 +0100
selftests/x86/ldt_gdt: Robustify against set_thread_area() and LAR oddities
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@xxxxxxxxxx>
Cc: Borislav Petkov <bpetkov@xxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Fixes: 5b781c7e317f ("x86/tls: Forcibly set the accessed bit in TLS segments")
Link: http://lkml.kernel.org/r/b82f3f89c034b53580970ac865139fd8863f44e2.1509794321.git.luto@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
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 961e3ee..b033433 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++;
--
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