Commit be04a6d1 authored by Will Deacon's avatar Will Deacon Committed by Catalin Marinas

arm64: use RET instruction for exiting the trampoline

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: default avatarWill Deacon <will.deacon@arm.com>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent 3b3b6810
......@@ -1029,6 +1029,14 @@ alternative_else_nop_endif
.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
......@@ -1041,7 +1049,7 @@ alternative_insn isb, nop, ARM64_WORKAROUND_QCOM_FALKOR_E1003
msr vbar_el1, x30
add x30, x30, #(1b - tramp_vectors)
isb
br x30
ret
.endm
.macro tramp_exit, regsize = 64
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment