Commit 346edd61 authored Apr 12, 2018 by Mark Rutland Committed by Greg Kroah-Hartman Apr 20, 2018

arm64: uaccess: Prevent speculative use of the current addr_limit




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]
Tested-by: Greg Hackmann <ghackmann@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent f3ed64a6

arch/arm64/include/asm/uaccess.h

+7 −0

Original line number	Diff line number	Diff line
		@@ -67,6 +67,13 @@ 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.