linux-kernel - Re: [PATCH v2 11/11] arm64: Implement branch predictor hardening for affected Cortex-A CPUs

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Date:   Fri, 05 Jan 2018 14:46:37 +0000
From:   James Morse <james.morse@....com>
To:     Will Deacon <will.deacon@....com>, marc.zyngier@....com
CC:     linux-arm-kernel@...ts.infradead.org, catalin.marinas@....com,
        ard.biesheuvel@...aro.org, lorenzo.pieralisi@....com,
        christoffer.dall@...aro.org, linux-kernel@...r.kernel.org,
        labbott@...hat.com
Subject: Re: [PATCH v2 11/11] arm64: Implement branch predictor hardening
 for affected Cortex-A CPUs

Hi Marc, Will,

(SOB-chain suggests a missing From: tag on this and patch 7)

On 05/01/18 13:12, Will Deacon wrote:
> Cortex-A57, A72, A73 and A75 are susceptible to branch predictor aliasing
> and can theoretically be attacked by malicious code.
> 
> This patch implements a PSCI-based mitigation for these CPUs when available.
> The call into firmware will invalidate the branch predictor state, preventing
> any malicious entries from affecting other victim contexts.
> 
> Signed-off-by: Marc Zyngier <marc.zyngier@....com>
> Signed-off-by: Will Deacon <will.deacon@....com>

> diff --git a/arch/arm64/kernel/bpi.S b/arch/arm64/kernel/bpi.S
> index 06a931eb2673..2e9146534174 100644
> --- a/arch/arm64/kernel/bpi.S
> +++ b/arch/arm64/kernel/bpi.S
> @@ -53,3 +53,27 @@ ENTRY(__bp_harden_hyp_vecs_start)
>  	vectors __kvm_hyp_vector
>  	.endr
>  ENTRY(__bp_harden_hyp_vecs_end)
> +ENTRY(__psci_hyp_bp_inval_start)

> +	sub	sp, sp, #(8 * 18)

Where does 18 come from? Isn't this storing 9 sets of 16 bytes?


> +	stp	x16, x17, [sp, #(16 * 0)]
> +	stp	x14, x15, [sp, #(16 * 1)]
> +	stp	x12, x13, [sp, #(16 * 2)]
> +	stp	x10, x11, [sp, #(16 * 3)]
> +	stp	x8, x9, [sp, #(16 * 4)]
> +	stp	x6, x7, [sp, #(16 * 5)]
> +	stp	x4, x5, [sp, #(16 * 6)]
> +	stp	x2, x3, [sp, #(16 * 7)]

> +	stp	x0, x1, [sp, #(18 * 8)]

16->18 typo?


> +	mov	x0, #0x84000000
> +	smc	#0
> +	ldp	x16, x17, [sp, #(16 * 0)]
> +	ldp	x14, x15, [sp, #(16 * 1)]
> +	ldp	x12, x13, [sp, #(16 * 2)]
> +	ldp	x10, x11, [sp, #(16 * 3)]
> +	ldp	x8, x9, [sp, #(16 * 4)]
> +	ldp	x6, x7, [sp, #(16 * 5)]
> +	ldp	x4, x5, [sp, #(16 * 6)]
> +	ldp	x2, x3, [sp, #(16 * 7)]

> +	ldp	x0, x1, [sp, #(18 * 8)]
> +	add	sp, sp, #(8 * 18)

(and here?)

> +ENTRY(__psci_hyp_bp_inval_end)


Thanks,

James