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Message-Id: <1519633227-29832-14-git-send-email-alex.shi@linaro.org>
Date: Mon, 26 Feb 2018 16:19:47 +0800
From: Alex Shi <alex.shi@...aro.org>
To: Marc Zyngier <marc.zyngier@....com>,
Will Deacon <will.deacon@....com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Catalin Marinas <catalin.marinas@....com>,
stable@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org (moderated list:ARM64 PORT
(AARCH64 ARCHITECTURE)), linux-kernel@...r.kernel.org (open list)
Subject: [PATCH 13/52] arm64: uaccess: Prevent speculative use of the current addr_limit
From: Will Deacon <will.deacon@....com>
commit c2f0ad4fc089 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@....com>
Signed-off-by: Will Deacon <will.deacon@....com>
Signed-off-by: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Alex Shi <alex.shi@...aro.org>
Conflicts:
no set_thread_flag(TIF_FSCHECK) in arch/arm64/include/asm/uaccess.h
---
arch/arm64/include/asm/uaccess.h | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 3531fec..00025c5 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -71,6 +71,13 @@ 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.
*/
--
2.7.4
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