Commit 1ccaee9d authored Feb 05, 2018 by Will Deacon Committed by Greg Kroah-Hartman Feb 16, 2018

arm64: uaccess: Prevent speculative use of the current addr_limit




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@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 7a51d7d2

arch/arm64/include/asm/uaccess.h

+7 −0

Original line number	Diff line number	Diff line
		@@ -42,6 +42,13 @@ 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();

		/* On user-mode return, check fs is correct */
		set_thread_flag(TIF_FSCHECK);