82 lines
2.5 KiB
Diff
82 lines
2.5 KiB
Diff
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Andy Lutomirski <luto@kernel.org>
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Date: Wed, 26 Jul 2017 07:16:30 -0700
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Subject: [PATCH] x86/ldt/64: Refresh DS and ES when modify_ldt changes an
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entry
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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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On x86_32, modify_ldt() implicitly refreshes the cached DS and ES
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segments because they are refreshed on return to usermode.
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On x86_64, they're not refreshed on return to usermode. To improve
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determinism and match x86_32's behavior, refresh them when we update
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the LDT.
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This avoids a situation in which the DS points to a descriptor that is
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changed but the old cached segment persists until the next reschedule.
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If this happens, then the user-visible state will change
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nondeterministically some time after modify_ldt() returns, which is
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unfortunate.
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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: Chang Seok <chang.seok.bae@intel.com>
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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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Signed-off-by: Ingo Molnar <mingo@kernel.org>
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(cherry picked from commit a632375764aa25c97b78beb56c71b0ba59d1cf83)
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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 295cb0b06150958ec84ee4b8844ef7e389e22c4e)
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Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
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---
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arch/x86/kernel/ldt.c | 21 +++++++++++++++++++++
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1 file changed, 21 insertions(+)
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diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c
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index a870910c8565..f0e64db18ac8 100644
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--- a/arch/x86/kernel/ldt.c
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+++ b/arch/x86/kernel/ldt.c
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@@ -21,6 +21,25 @@
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#include <asm/mmu_context.h>
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#include <asm/syscalls.h>
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+static void refresh_ldt_segments(void)
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+{
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+#ifdef CONFIG_X86_64
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+ unsigned short sel;
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+
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+ /*
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+ * Make sure that the cached DS and ES descriptors match the updated
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+ * LDT.
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+ */
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+ savesegment(ds, sel);
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+ if ((sel & SEGMENT_TI_MASK) == SEGMENT_LDT)
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+ loadsegment(ds, sel);
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+
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+ savesegment(es, sel);
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+ if ((sel & SEGMENT_TI_MASK) == SEGMENT_LDT)
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+ loadsegment(es, sel);
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+#endif
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+}
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+
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/* context.lock is held for us, so we don't need any locking. */
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static void flush_ldt(void *__mm)
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{
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@@ -32,6 +51,8 @@ static void flush_ldt(void *__mm)
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pc = &mm->context;
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set_ldt(pc->ldt->entries, pc->ldt->nr_entries);
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+
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+ refresh_ldt_segments();
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}
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/* The caller must call finalize_ldt_struct on the result. LDT starts zeroed. */
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--
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2.14.2
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