[PATCH 6.12 485/567] lib/crypto: riscv/chacha: Avoid s0/fp register

Greg Kroah-Hartman
2026-01-06T17:41:09Z

From: Vivian Wang <wangruikang@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@iscas.ac.cn>
Fixes: bb54668837a0 ("crypto: riscv - add vector crypto accelerated ChaCha20")
Cc: stable@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@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/riscv/crypto/chacha-riscv64-zvkb.S | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)

--- a/arch/riscv/crypto/chacha-riscv64-zvkb.S
+++ b/arch/riscv/crypto/chacha-riscv64-zvkb.S
@@ -60,7 +60,8 @@
#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
@@ -141,7 +142,6 @@ 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)
@@ -277,7 +277,6 @@ SYM_FUNC_START(chacha20_zvkb)
add INP, INP, TMP
bnez LEN, .Lblock_loop

- ld s0, 0(sp)
ld s1, 8(sp)
ld s2, 16(sp)
ld s3, 24(sp)