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From: Andy Lutomirski <luto@kernel.org>
To: X86 ML <x86@kernel.org>
Cc: Borislav Petkov <bpetkov@suse.de>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Andy Lutomirski <luto@kernel.org>
Subject: [PATCH 2/5] selftests/x86/ldt_gdt: Robustify against set_thread_area() and LAR oddities
Date: Sat,  4 Nov 2017 04:19:49 -0700
Message-ID: <b82f3f89c034b53580970ac865139fd8863f44e2.1509794321.git.luto@kernel.org> (raw)
In-Reply-To: <cover.1509794321.git.luto@kernel.org>
In-Reply-To: <cover.1509794321.git.luto@kernel.org>

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.

Fixes: 5b781c7e317f ("x86/tls: Forcibly set the accessed bit in TLS segments")
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 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 b9a22f18566a..b2c54f4673f2 100644
--- a/tools/testing/selftests/x86/ldt_gdt.c
+++ b/tools/testing/selftests/x86/ldt_gdt.c
@@ -114,7 +114,15 @@ 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++;
-- 
2.13.6

  parent reply index

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-11-04 11:19 [PATCH 0/5] Minor selftests improvements Andy Lutomirski
2017-11-04 11:19 ` [PATCH 1/5] selftests/x86/protection_keys: Fix syscall NR redefinition warnings Andy Lutomirski
2017-11-07 10:16   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2017-11-04 11:19 ` Andy Lutomirski [this message]
2017-11-07 10:17   ` [tip:x86/asm] selftests/x86/ldt_gdt: Robustify against set_thread_area() and LAR oddities tip-bot for Andy Lutomirski
2017-11-04 11:19 ` [PATCH 3/5] selftests/x86/ldt_gdt: Add infrastructure to test set_thread_area() Andy Lutomirski
2017-11-07 10:17   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2017-11-04 11:19 ` [PATCH 4/5] selftests/x86/ldt_gdt: Run most existing LDT test cases against the GDT as well Andy Lutomirski
2017-11-07 10:17   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2017-11-04 11:19 ` [PATCH 5/5] selftests/x86/ldt_get: Add a few additional tests for limits Andy Lutomirski
2017-11-07 10:18   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2017-11-07 10:13 ` [PATCH 0/5] Minor selftests improvements Ingo Molnar

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