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arm64: uaccess: Prevent speculative use of the current addr_limit

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From: Will Deacon <will.deacon@arm.com>

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: 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>
This commit is contained in:
Mark Rutland
2018-04-12 12:11:03 +01:00
committed by Greg Kroah-Hartman
parent f3ed64a627
commit 346edd61ce
1 changed files with 7 additions and 0 deletions
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7
arch/arm64/include/asm/uaccess.h
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@@ -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.