Unverified Commit 61119394 authored by Celeste Liu's avatar Celeste Liu Committed by Palmer Dabbelt
Browse files

riscv: entry: always initialize regs->a0 to -ENOSYS 



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.

Fixes: 52449c17 ("riscv: entry: set a0 = -ENOSYS only when syscall != -1")
Reported-by: default avatar"Dmitry V. Levin" <ldv@strace.io>
Reviewed-by: default avatarBjörn Töpel <bjorn@rivosinc.com>
Cc: stable@vger.kernel.org
Signed-off-by: default avatarCeleste Liu <CoelacanthusHex@gmail.com>
Link: https://lore.kernel.org/r/20240627142338.5114-2-CoelacanthusHex@gmail.com


Signed-off-by: default avatarPalmer Dabbelt <palmer@rivosinc.com>
parent ee9a6839

arch/riscv/kernel/traps.c

+2 −2
Original line number Diff line number Diff line
@@ -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).