[PATCH AUTOSEL 6.11 38/76] riscv: avoid Imbalance in RAS

Sasha Levin
2024-10-04T18:19:41Z

From: Jisheng Zhang <jszhang@kernel.org>

[ Upstream commit 8f1534e7440382d118c3d655d3a6014128b2086d ]

Inspired by[1], modify the code to remove the code of modifying ra to
avoid imbalance RAS (return address stack) which may lead to incorret
predictions on return.

Link: https://lore.kernel.org/linux-riscv/20240607061335.2197383-1-cyrilbur@tenstorrent.com/ [1]
Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Reviewed-by: Cyril Bur <cyrilbur@tenstorrent.com>
Link: https://lore.kernel.org/r/20240720170659.1522-1-jszhang@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/riscv/kernel/entry.S | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
index ac2e908d4418d..fefb8e7d957a0 100644
--- a/arch/riscv/kernel/entry.S
+++ b/arch/riscv/kernel/entry.S
@@ -239,8 +239,8 @@ SYM_CODE_START(ret_from_fork)
jalr s0
1:
move a0, sp /* pt_regs */
- la ra, ret_from_exception
- tail syscall_exit_to_user_mode
+ call syscall_exit_to_user_mode
+ j ret_from_exception
SYM_CODE_END(ret_from_fork)

#ifdef CONFIG_IRQ_STACKS
--
2.43.0