[PATCH 6.12] lib/crypto: riscv/chacha: Avoid s0/fp register

[Eric Biggers]

From: Vivian Wang <wangruikang at iscas.ac.cn>

commit 43169328c7b4623b54b7713ec68479cebda5465f upstream.

In chacha_zvkb, avoid using the s0 register, which is the frame pointer,
by reallocating KEY0 to t5. This makes stack traces available if e.g. a
crash happens in chacha_zvkb.

No frame pointer maintenance is otherwise required since this is a leaf
function.

Signed-off-by: Vivian Wang <wangruikang at iscas.ac.cn>
Fixes: bb54668837a0 ("crypto: riscv - add vector crypto accelerated ChaCha20")
Cc: stable at vger.kernel.org
Link: https://lore.kernel.org/r/20251202-riscv-chacha_zvkb-fp-v2-1-7bd00098c9dc@iscas.ac.cn
Signed-off-by: Eric Biggers <ebiggers at kernel.org>
---
 arch/riscv/crypto/chacha-riscv64-zvkb.S | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/crypto/chacha-riscv64-zvkb.S b/arch/riscv/crypto/chacha-riscv64-zvkb.S
index bf057737ac69..fbef93503571 100644
--- a/arch/riscv/crypto/chacha-riscv64-zvkb.S
+++ b/arch/riscv/crypto/chacha-riscv64-zvkb.S
@@ -58,11 +58,12 @@
 #define CONSTS3		t0
 #define TMP		t1
 #define VL		t2
 #define STRIDE		t3
 #define NROUNDS		t4
-#define KEY0		s0
+#define KEY0		t5
+// Avoid s0/fp to allow for unwinding
 #define KEY1		s1
 #define KEY2		s2
 #define KEY3		s3
 #define KEY4		s4
 #define KEY5		s5
@@ -139,11 +140,10 @@
 // The counter is treated as 32-bit, following the RFC7539 convention.
 SYM_FUNC_START(chacha20_zvkb)
 	srli		LEN, LEN, 6	// Bytes to blocks
 
 	addi		sp, sp, -96
-	sd		s0, 0(sp)
 	sd		s1, 8(sp)
 	sd		s2, 16(sp)
 	sd		s3, 24(sp)
 	sd		s4, 32(sp)
 	sd		s5, 40(sp)
@@ -275,11 +275,10 @@ SYM_FUNC_START(chacha20_zvkb)
 	slli		TMP, VL, 6
 	add		OUTP, OUTP, TMP
 	add		INP, INP, TMP
 	bnez		LEN, .Lblock_loop
 
-	ld		s0, 0(sp)
 	ld		s1, 8(sp)
 	ld		s2, 16(sp)
 	ld		s3, 24(sp)
 	ld		s4, 32(sp)
 	ld		s5, 40(sp)

base-commit: 567bd8cbc2fe6b28b78864cbbbc41b0d405eb83c
-- 
2.52.0