From 51de580e8e70ad1bf23a68384a6a3be5bda719f5 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Tue, 14 Nov 2017 16:15:59 +0000 Subject: [PATCH] arm64: use RET instruction for exiting the trampoline commit be04a6d1126b 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 Signed-off-by: Catalin Marinas Signed-off-by: Alex Shi --- arch/arm64/kernel/entry.S | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 3abaa5d79b86..3d8728009aa2 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -902,6 +902,14 @@ __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 @@ -914,7 +922,7 @@ __ni_sys_trace: msr vbar_el1, x30 add x30, x30, #(1b - tramp_vectors) isb - br x30 + ret .endm .macro tramp_exit, regsize = 64 -- 2.17.1