Commit 68a65ce7 authored by Will Deacon's avatar Will Deacon Committed by Greg Kroah-Hartman
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arm64: use RET instruction for exiting the trampoline

Commit be04a6d1


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 <>
Signed-off-by: default avatarCatalin Marinas <>
Signed-off-by: default avatarArd Biesheuvel <>
Signed-off-by: default avatarGreg Kroah-Hartman <>
parent 3882b5f6
......@@ -981,6 +981,14 @@ alternative_else_nop_endif
.if \regsize == 64
msr tpidrro_el0, x30 // Restored in kernel_ventry
* 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 .
tramp_map_kernel x30
adr x30, tramp_vectors + PAGE_SIZE
......@@ -993,7 +1001,7 @@ alternative_insn isb, nop, ARM64_WORKAROUND_QCOM_FALKOR_E1003
msr vbar_el1, x30
add x30, x30, #(1b - tramp_vectors)
br x30
.macro tramp_exit, regsize = 64
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