[v4.9.y,07/42] arm64: uaccess: Prevent speculative use of the current addr_limit

Message ID 20180412111138.40990-8-mark.rutland@arm.com
State New
Headers show
Series
  • arm64 spectre patches
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Commit Message

Mark Rutland April 12, 2018, 11:11 a.m.
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: Mark Rutland <mark.rutland@arm.com> [v4.9 backport]

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

-- 
2.11.0

Patch

diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index a9db051b967f..900397e73fa6 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -68,6 +68,13 @@  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();
+
+	/*
 	 * Enable/disable UAO so that copy_to_user() etc can access
 	 * kernel memory with the unprivileged instructions.
 	 */