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arm64: use RET instruction for exiting the trampoline

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commit be04a6d112 upstream.

Speculation attacks against the entry trampoline can potentially resteer
the speculative instruction stream through the indirect branch and into
arbitrary gadgets within the kernel.

This patch defends against these attacks by forcing a misprediction
through the return stack: a dummy BL instruction loads an entry into
the stack, so that the predicted program flow of the subsequent RET
instruction is to a branch-to-self instruction which is finally resolved
as a branch to the kernel vectors with speculation suppressed.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Alex Shi <alex.shi@linaro.org> [v4.9 backport]
Signed-off-by: Mark Rutland <mark.rutland@arm.com> [v4.9 backport]
Tested-by: Will Deacon <will.deacon@arm.com>
Tested-by: Greg Hackmann <ghackmann@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Will Deacon
2018-04-03 12:09:11 +01:00
committed by Greg Kroah-Hartman
parent 96750422f8
commit f6af5324fb
1 changed files with 9 additions and 1 deletions
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10
arch/arm64/kernel/entry.S
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@@ -880,6 +880,14 @@ __ni_sys_trace:
.if \regsize == 64
msr tpidrro_el0, x30 // Restored in kernel_ventry
.endif
/*
* Defend against branch aliasing attacks by pushing a dummy
* entry onto the return stack and using a RET instruction to
* enter the full-fat kernel vectors.
*/
bl 2f
b .
2:
tramp_map_kernel x30
#ifdef CONFIG_RANDOMIZE_BASE
adr x30, tramp_vectors + PAGE_SIZE
@@ -892,7 +900,7 @@ __ni_sys_trace:
msr vbar_el1, x30
add x30, x30, #(1b - tramp_vectors)
isb
br x30
ret
.endm
.macro tramp_exit, regsize = 64