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arm64: uaccess: Prevent speculative use of the current addr_limit

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Commit c2f0ad4fc0 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>
This commit is contained in:
Will Deacon 2018-02-05 15:34:21 +00:00 committed by Greg Kroah-Hartman
parent 7a51d7d2f7
commit 1ccaee9dea
1 changed files with 7 additions and 0 deletions
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7
arch/arm64/include/asm/uaccess.h
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@ -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);