linux-kernel - [PATCH] lib/crypto: riscv/chacha: Maintain a frame pointer

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Message-Id: <20251130-riscv-chacha_zvkb-fp-v1-1-68ef7a6d477a@iscas.ac.cn>
Date: Sun, 30 Nov 2025 18:23:50 +0800
From: Vivian Wang <wangruikang@...as.ac.cn>
To: Jerry Shih <jerry.shih@...ive.com>, Eric Biggers <ebiggers@...nel.org>, 
 "Jason A. Donenfeld" <Jason@...c4.com>, Ard Biesheuvel <ardb@...nel.org>, 
 Paul Walmsley <pjw@...nel.org>, Palmer Dabbelt <palmer@...belt.com>, 
 Albert Ou <aou@...s.berkeley.edu>, Alexandre Ghiti <alex@...ti.fr>
Cc: linux-crypto@...r.kernel.org, linux-riscv@...ts.infradead.org, 
 linux-kernel@...r.kernel.org, Vivian Wang <wangruikang@...as.ac.cn>
Subject: [PATCH] lib/crypto: riscv/chacha: Maintain a frame pointer

crypto_zvkb doesn't maintain a frame pointer and also uses s0, which
means that if it crashes we don't get a stack trace. Modify prologue and
epilogue to maintain a frame pointer as -fno-omit-frame-pointer would.
Also reallocate registers to match.

Signed-off-by: Vivian Wang <wangruikang@...as.ac.cn>
---
Found while diagnosing a crypto_zvkb "load address misaligned" crash [1]

[1]: https://lore.kernel.org/r/b3cfcdac-0337-4db0-a611-258f2868855f@iscas.ac.cn/
---
 lib/crypto/riscv/chacha-riscv64-zvkb.S | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/lib/crypto/riscv/chacha-riscv64-zvkb.S b/lib/crypto/riscv/chacha-riscv64-zvkb.S
index b777d0b4e379..dc4e45759d14 100644
--- a/lib/crypto/riscv/chacha-riscv64-zvkb.S
+++ b/lib/crypto/riscv/chacha-riscv64-zvkb.S
@@ -60,7 +60,7 @@
 #define VL		t2
 #define STRIDE		t3
 #define ROUND_CTR	t4
-#define KEY0		s0
+#define KEY0		t5
 #define KEY1		s1
 #define KEY2		s2
 #define KEY3		s3
@@ -142,8 +142,7 @@
 // the original Salsa20 paper which uses a 64-bit counter in state->x[12..13].
 // The updated 32-bit counter is written back to state->x[12] before returning.
 SYM_FUNC_START(chacha_zvkb)
-	addi		sp, sp, -96
-	sd		s0, 0(sp)
+	addi		sp, sp, -112
 	sd		s1, 8(sp)
 	sd		s2, 16(sp)
 	sd		s3, 24(sp)
@@ -155,6 +154,10 @@ SYM_FUNC_START(chacha_zvkb)
 	sd		s9, 72(sp)
 	sd		s10, 80(sp)
 	sd		s11, 88(sp)
+	sd		fp, 96(sp)
+	sd		ra, 104(sp)
+
+	addi		fp, sp, 112

 	li		STRIDE, 64

@@ -280,7 +283,6 @@ SYM_FUNC_START(chacha_zvkb)
 	bnez		NBLOCKS, .Lblock_loop

 	sw		COUNTER, 48(STATEP)
-	ld		s0, 0(sp)
 	ld		s1, 8(sp)
 	ld		s2, 16(sp)
 	ld		s3, 24(sp)
@@ -292,6 +294,7 @@ SYM_FUNC_START(chacha_zvkb)
 	ld		s9, 72(sp)
 	ld		s10, 80(sp)
 	ld		s11, 88(sp)
-	addi		sp, sp, 96
+	ld		fp, 96(sp)
+	addi		sp, sp, 112
 	ret
 SYM_FUNC_END(chacha_zvkb)

---
base-commit: 3a8660878839faadb4f1a6dd72c3179c1df56787
change-id: 20251130-riscv-chacha_zvkb-fp-5644ed88b1a2

Best regards,
-- 
Vivian "dramforever" Wang