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Date: Fri, 23 Feb 2018 19:26:51 +0100
From: Greg Kroah-Hartman <>
Cc: Greg Kroah-Hartman <>,,
	Linus Torvalds <>,
	Dan Williams <>,
	Thomas Gleixner <>,,,
	Andy Lutomirski <>,,
	David Woodhouse <>,
	Jack Wang <>
Subject: [PATCH 4.4 178/193] x86/syscall: Sanitize syscall table de-references under speculation

4.4-stable review patch.  If anyone has any objections, please let me know.


From: Dan Williams <>

(cherry picked from commit 2fbd7af5af8665d18bcefae3e9700be07e22b681)

The syscall table base is a user controlled function pointer in kernel
space. Use array_index_nospec() to prevent any out of bounds speculation.

While retpoline prevents speculating into a userspace directed target it
does not stop the pointer de-reference, the concern is leaking memory
relative to the syscall table base, by observing instruction cache

Reported-by: Linus Torvalds <>
Signed-off-by: Dan Williams <>
Signed-off-by: Thomas Gleixner <>
Cc: Andy Lutomirski <>
Signed-off-by: David Woodhouse <>
[jwang: port to 4.4, no syscall_64]
Signed-off-by: Jack Wang <>
Signed-off-by: Greg Kroah-Hartman <>
 arch/x86/entry/common.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -20,6 +20,7 @@
 #include <linux/export.h>
 #include <linux/context_tracking.h>
 #include <linux/user-return-notifier.h>
+#include <linux/nospec.h>
 #include <linux/uprobes.h>
 #include <asm/desc.h>
@@ -381,6 +382,7 @@ __always_inline void do_syscall_32_irqs_
 	if (likely(nr < IA32_NR_syscalls)) {
+		nr = array_index_nospec(nr, IA32_NR_syscalls);
 		 * It's possible that a 32-bit syscall implementation
 		 * takes a 64-bit parameter but nonetheless assumes that

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