[4.9,05/16] ARM: 8794/1: uaccess: Prevent speculative use of the current addr_limit

Message ID 20190214144930.27539-6-dave.long@linaro.org
State New
Headers show
  • V4.9 backport of more 32-bit arm spectre patches
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Commit Message

David Long Feb. 14, 2019, 2:49 p.m.
From: Julien Thierry <julien.thierry@arm.com>

Commit 621afc677465db231662ed126ae1f355bf8eac47 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

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

Porting commit c2f0ad4fc089cff8 ("arm64: uaccess: Prevent speculative use
of the current addr_limit").

Signed-off-by: Julien Thierry <julien.thierry@arm.com>

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

Signed-off-by: David A. Long <dave.long@linaro.org>

 arch/arm/include/asm/uaccess.h | 8 ++++++++
 1 file changed, 8 insertions(+)



diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h
index 7b17460127fd..9ae888775743 100644
--- a/arch/arm/include/asm/uaccess.h
+++ b/arch/arm/include/asm/uaccess.h
@@ -99,6 +99,14 @@  extern int __put_user_bad(void);
 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();