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

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Date:   Mon,  5 Oct 2020 22:48:54 -0500
From:   Jeremy Linton <jeremy.linton@....com>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     linux-crypto@...r.kernel.org, broonie@...nel.org, ardb@...nel.org,
        will@...nel.org, catalin.marinas@....com, davem@...emloft.net,
        herbert@...dor.apana.org.au, linux-kernel@...r.kernel.org,
        Jeremy Linton <jeremy.linton@....com>
Subject: [BUG][PATCH] crypto: arm64: Avoid indirect branch to bti_c

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")
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]
-- 
2.25.4