FAILED: patch "[PATCH] riscv: entry: always initialize regs->a0 to -ENOSYS" failed to apply to 6.6-stable tree

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 61119394631f219e23ce98bcc3eb993a64a8ea64
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2024081917-flanked-clear-e564@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

61119394631f ("riscv: entry: always initialize regs->a0 to -ENOSYS") 05d450aabd73 ("riscv: Support RANDOMIZE_KSTACK_OFFSET")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 61119394631f219e23ce98bcc3eb993a64a8ea64 Mon Sep 17 00:00:00 2001
From: Celeste Liu <[email protected]>
Date: Thu, 27 Jun 2024 22:23:39 +0800
Subject: [PATCH] riscv: entry: always initialize regs->a0 to -ENOSYS
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Otherwise when the tracer changes syscall number to -1, the kernel fails to initialize a0 with -ENOSYS and subsequently fails to return the error code of the failed syscall to userspace. For example, it will break strace syscall tampering.

index 05a16b1f0aee..51ebfd23e007 100644
@@ -319,6 +319,7 @@ void do_trap_ecall_u(struct pt_regs *regs)
 
 		regs->epc += 4;
 		regs->orig_a0 = regs->a0;
+		regs->a0 = -ENOSYS;
 
 		riscv_v_vstate_discard(regs);
 

@@ -328,8 +329,7 @@ void do_trap_ecall_u(struct pt_regs *regs)
 
 		if (syscall >= 0 && syscall < NR_syscalls)
 			syscall_handler(regs, syscall);
-		else if (syscall != -1)
-			regs->a0 = -ENOSYS;
+
 		/*
 		 * Ultimately, this value will get limited by KSTACK_OFFSET_MAX(),
 		 * so the maximum stack offset is 1k bytes (10 bits).

From: Celeste Liu <[email protected]>

Otherwise when the tracer changes syscall number to -1, the kernel fails to initialize a0 with -ENOSYS and subsequently fails to return the error code of the failed syscall to userspace. For example, it will break strace syscall tampering.

---
 arch/riscv/kernel/traps.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

index 67d0073fb624..2158b7a65d74 100644
@@ -311,6 +311,7 @@ asmlinkage __visible __trap_section void do_trap_ecall_u(struct pt_regs *regs)
 
 		regs->epc += 4;
 		regs->orig_a0 = regs->a0;
+		regs->a0 = -ENOSYS;
 
 		riscv_v_vstate_discard(regs);
 

@@ -318,8 +319,6 @@ asmlinkage __visible __trap_section void do_trap_ecall_u(struct pt_regs *regs)
 
 		if (syscall >= 0 && syscall < NR_syscalls)
 			syscall_handler(regs, syscall);
-		else if (syscall != -1)
-			regs->a0 = -ENOSYS;
 
 		syscall_exit_to_user_mode(regs);
 	} else {

2.46.0