Commit 68a65ce7 authored Nov 14, 2017 by Will Deacon Committed by Greg Kroah-Hartman Feb 16, 2018

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 <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 3882b5f6

arch/arm64/kernel/entry.S

+9 −1

Original line number	Original line	Diff line number	Diff line
	@@ -981,6 +981,14 @@ alternative_else_nop_endif
	.if \regsize == 64		.if \regsize == 64
	msr tpidrro_el0, x30 // Restored in kernel_ventry		msr tpidrro_el0, x30 // Restored in kernel_ventry
	.endif		.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		tramp_map_kernel x30
	#ifdef CONFIG_RANDOMIZE_BASE		#ifdef CONFIG_RANDOMIZE_BASE
	adr x30, tramp_vectors + PAGE_SIZE		adr x30, tramp_vectors + PAGE_SIZE
	@@ -993,7 +1001,7 @@ alternative_insn isb, nop, ARM64_WORKAROUND_QCOM_FALKOR_E1003
	msr vbar_el1, x30		msr vbar_el1, x30
	add x30, x30, #(1b - tramp_vectors)		add x30, x30, #(1b - tramp_vectors)
	isb		isb
	br x30		ret
	.endm		.endm

	.macro tramp_exit, regsize = 64		.macro tramp_exit, regsize = 64