[ARM64,v4.4,V3,07/44] arm64: uaccess: Prevent speculative use of the current addr_limit

Message ID dbe69b13f77052abf5d342b2775b1ebdbcce241a.1567077734.git.viresh.kumar@linaro.org
State New
Headers show
Series
  • V4.4 backport of arm64 Spectre patches
Related show

Commit Message

Viresh Kumar Aug. 29, 2019, 11:33 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: Viresh Kumar <viresh.kumar@linaro.org>

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

-- 
2.21.0.rc0.269.g1a574e7a288b

Comments

Mark Rutland Aug. 30, 2019, 9:40 a.m. | #1
On Thu, Aug 29, 2019 at 05:03:52PM +0530, Viresh Kumar wrote:
> 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>


Reviewed-by: Mark Rutland <mark.rutland@arm.com> [v4.4 backport]


Mark.

> ---

>  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 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))

> -- 

> 2.21.0.rc0.269.g1a574e7a288b

>

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))