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[v4.4,08/45] arm64: uaccess: Prevent speculative use of the current addr_limit

Message ID d74517ad6c0ca7d077063c18cd1930aa6bcb503c.1560480942.git.viresh.kumar@linaro.org
State Superseded
Headers show
Series V4.4 backport of arm64 Spectre patches | expand

Commit Message

Viresh Kumar June 14, 2019, 3:07 a.m. UTC 
From: Will Deacon <will.deacon@arm.com>


commit c2f0ad4fc089cff81cef6a13d04b399980ecbfcc upstream.

A mispredicted conditional call to set_fs could result in the wrong
addr_limit being forwarded under speculation to a subsequent access_ok
check, potentially forming part of a spectre-v1 attack using uaccess
routines.

This patch prevents this forwarding from taking place, but putting heavy
barriers in set_fs after writing the addr_limit.

Reviewed-by: Mark Rutland <mark.rutland@arm.com>

Signed-off-by: Will Deacon <will.deacon@arm.com>

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

---
 arch/arm64/include/asm/uaccess.h | 7 +++++++
 1 file changed, 7 insertions(+)

-- 
2.21.0.rc0.269.g1a574e7a288b
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Patch

diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 75363d723262..fc11c50af558 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -62,6 +62,13 @@  extern int fixup_exception(struct pt_regs *regs);
 static inline void set_fs(mm_segment_t fs)
 {
 	current_thread_info()->addr_limit = fs;
+
+	/*
+	 * Prevent a mispredicted conditional call to set_fs from forwarding
+	 * the wrong address limit to access_ok under speculation.
+	 */
+	dsb(nsh);
+	isb();
 }
 
 #define segment_eq(a, b)	((a) == (b))