[v2] riscv: avoid Imbalance in RAS

Commit Message

Jisheng Zhang July 20, 2024, 5:06 p.m. UTC

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/[e-mail]/ [1]
Signed-off-by: Jisheng Zhang <[e-mail]>
Reviewed-by: Cyril Bur <[e-mail]>
---

since v1:
 - make it a seperate patch
 - modify the commit msg, thank Deepak
 - collect Reviewed-by tag

 arch/riscv/kernel/entry.S | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Comments

[e-mail] Sept. 17, 2024, 1 p.m. UTC | #1

Hello:

This patch was applied to riscv/linux.git (for-next)
by Palmer Dabbelt <[e-mail]>:

On Sun, 21 Jul 2024 01:06:59 +0800 you wrote:
> 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/[e-mail]/ [1]
> Signed-off-by: Jisheng Zhang <[e-mail]>
> Reviewed-by: Cyril Bur <[e-mail]>
> 
> [...]

Here is the summary with links:
  - [v2] riscv: avoid Imbalance in RAS
    https://git.kernel.org/riscv/c/8f1534e74403

You are awesome, thank you!

Patch

diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
index c933460ed3e9..81dec627a8d4 100644
--- a/arch/riscv/kernel/entry.S
+++ b/arch/riscv/kernel/entry.S
@@ -235,8 +235,8 @@  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