linux-kernel - Re: [BUG][PATCH] crypto: arm64: Avoid indirect branch to bti

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Message-ID: <20201006082748.GB25305@willie-the-truck>
Date:   Tue, 6 Oct 2020 09:27:48 +0100
From:   Will Deacon <will@...nel.org>
To:     Jeremy Linton <jeremy.linton@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-crypto@...r.kernel.org,
        broonie@...nel.org, ardb@...nel.org, catalin.marinas@....com,
        davem@...emloft.net, herbert@...dor.apana.org.au,
        linux-kernel@...r.kernel.org
Subject: Re: [BUG][PATCH] crypto: arm64: Avoid indirect branch to bti_c

On Mon, Oct 05, 2020 at 10:48:54PM -0500, Jeremy Linton wrote:
> The AES code uses a 'br x7' as part of a function called by
> a macro. That branch needs a bti_j as a target. This results
> in a panic as seen below. Instead of trying to replace the branch
> target with a bti_jc, lets replace the indirect branch with a
> bl/ret, bl sequence that can target the existing bti_c.
> 
>   Bad mode in Synchronous Abort handler detected on CPU1, code 0x34000003 -- BTI
>   CPU: 1 PID: 265 Comm: cryptomgr_test Not tainted 5.8.11-300.fc33.aarch64 #1
>   pstate: 20400c05 (nzCv daif +PAN -UAO BTYPE=j-)
>   pc : aesbs_encrypt8+0x0/0x5f0 [aes_neon_bs]
>   lr : aesbs_xts_encrypt+0x48/0xe0 [aes_neon_bs]
>   sp : ffff80001052b730
> 
>   aesbs_encrypt8+0x0/0x5f0 [aes_neon_bs]
>    __xts_crypt+0xb0/0x2dc [aes_neon_bs]
>    xts_encrypt+0x28/0x3c [aes_neon_bs]
>   crypto_skcipher_encrypt+0x50/0x84
>   simd_skcipher_encrypt+0xc8/0xe0
>   crypto_skcipher_encrypt+0x50/0x84
>   test_skcipher_vec_cfg+0x224/0x5f0
>   test_skcipher+0xbc/0x120
>   alg_test_skcipher+0xa0/0x1b0
>   alg_test+0x3dc/0x47c
>   cryptomgr_test+0x38/0x60
> 
> Fixes: commit 0e89640b640d ("crypto: arm64 - Use modern annotations for assembly functions")

nit: the "commit" string shouldn't be here, and I think the linux-next
scripts will yell at us if we don't remove it.

> Signed-off-by: Jeremy Linton <jeremy.linton@....com>
> ---
>  arch/arm64/crypto/aes-neonbs-core.S | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/crypto/aes-neonbs-core.S b/arch/arm64/crypto/aes-neonbs-core.S
> index b357164379f6..32f53ebe5e2c 100644
> --- a/arch/arm64/crypto/aes-neonbs-core.S
> +++ b/arch/arm64/crypto/aes-neonbs-core.S
> @@ -788,7 +788,7 @@ SYM_FUNC_START_LOCAL(__xts_crypt8)
>  
>  0:	mov		bskey, x21
>  	mov		rounds, x22
> -	br		x7
> +	ret
>  SYM_FUNC_END(__xts_crypt8)
>  
>  	.macro		__xts_crypt, do8, o0, o1, o2, o3, o4, o5, o6, o7
> @@ -806,8 +806,8 @@ SYM_FUNC_END(__xts_crypt8)
>  	uzp1		v30.4s, v30.4s, v25.4s
>  	ld1		{v25.16b}, [x24]
>  
> -99:	adr		x7, \do8
> -	bl		__xts_crypt8
> +99:	bl		__xts_crypt8
> +	bl 		\do8
>  
>  	ldp		q16, q17, [sp, #.Lframe_local_offset]
>  	ldp		q18, q19, [sp, #.Lframe_local_offset + 32]

Acked-by: Will Deacon <will@...nel.org>

Catalin -- can you pick this for 5.9 please?

Will