2018-01-15 14:26:15 +03:00
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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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2018-01-06 17:13:39 +03:00
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From: Andy Lutomirski <luto@kernel.org>
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Date: Sat, 4 Nov 2017 04:19:49 -0700
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2018-01-15 14:26:15 +03:00
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Subject: [PATCH] selftests/x86/ldt_gdt: Robustify against set_thread_area()
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and LAR oddities
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2018-01-06 17:13:39 +03:00
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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CVE-2017-5754
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Bits 19:16 of LAR's result are undefined, and some upcoming
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improvements to the test case seem to trigger this. Mask off those
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bits to avoid spurious failures.
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commit 5b781c7e317f ("x86/tls: Forcibly set the accessed bit in TLS
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segments") adds a valid case in which LAR's output doesn't quite
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agree with set_thread_area()'s input. This isn't triggered in the
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test as is, but it will be if we start calling set_thread_area()
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with the accessed bit clear. Work around this discrepency.
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I've added a Fixes tag so that -stable can pick this up if neccesary.
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Signed-off-by: Andy Lutomirski <luto@kernel.org>
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Cc: Borislav Petkov <bpetkov@suse.de>
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Cc: Linus Torvalds <torvalds@linux-foundation.org>
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Cc: Peter Zijlstra <peterz@infradead.org>
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Cc: Thomas Gleixner <tglx@linutronix.de>
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Fixes: 5b781c7e317f ("x86/tls: Forcibly set the accessed bit in TLS segments")
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Link: http://lkml.kernel.org/r/b82f3f89c034b53580970ac865139fd8863f44e2.1509794321.git.luto@kernel.org
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Signed-off-by: Ingo Molnar <mingo@kernel.org>
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(cherry picked from commit d60ad744c9741586010d4bea286f09a063a90fbd)
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Signed-off-by: Andy Whitcroft <apw@canonical.com>
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Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
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(cherry picked from commit d4c2ffcf3efe0d9610919fd48f5a1a5e38c28c07)
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Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
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---
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tools/testing/selftests/x86/ldt_gdt.c | 10 +++++++++-
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1 file changed, 9 insertions(+), 1 deletion(-)
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diff --git a/tools/testing/selftests/x86/ldt_gdt.c b/tools/testing/selftests/x86/ldt_gdt.c
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index b9a22f18566a..b2c54f4673f2 100644
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--- a/tools/testing/selftests/x86/ldt_gdt.c
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+++ b/tools/testing/selftests/x86/ldt_gdt.c
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@@ -114,7 +114,15 @@ static void check_valid_segment(uint16_t index, int ldt,
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return;
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}
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- if (ar != expected_ar) {
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+ /* The SDM says "bits 19:16 are undefined". Thanks. */
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+ ar &= ~0xF0000;
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+
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+ /*
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+ * NB: Different Linux versions do different things with the
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+ * accessed bit in set_thread_area().
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+ */
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+ if (ar != expected_ar &&
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+ (ldt || ar != (expected_ar | AR_ACCESSED))) {
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printf("[FAIL]\t%s entry %hu has AR 0x%08X but expected 0x%08X\n",
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(ldt ? "LDT" : "GDT"), index, ar, expected_ar);
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nerrs++;
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--
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2.14.2
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