]> www.infradead.org Git - users/dwmw2/linux.git/commitdiff
riscv: entry: Save a0 prior syscall_enter_from_user_mode()
authorBjörn Töpel <bjorn@rivosinc.com>
Mon, 3 Apr 2023 06:52:07 +0000 (08:52 +0200)
committerPalmer Dabbelt <palmer@rivosinc.com>
Tue, 11 Apr 2023 15:25:29 +0000 (08:25 -0700)
The RISC-V calling convention passes the first argument, and the
return value in the a0 register. For this reason, the a0 register
needs some extra care; When handling syscalls, the a0 register is
saved into regs->orig_a0, so a0 can be properly restored for,
e.g. interrupted syscalls.

This functionality was broken with the introduction of the generic
entry patches. Here, a0 was saved into orig_a0 after calling
syscall_enter_from_user_mode(), which can change regs->a0 for some
paths, incorrectly restoring a0.

This is resolved, by saving a0 prior doing the
syscall_enter_from_user_mode() call.

Fixes: f0bddf50586d ("riscv: entry: Convert to generic entry")
Reviewed-by: Heiko Stuebner <heiko.stuebner@vrull.eu>
Tested-by: Heiko Stuebner <heiko.stuebner@vrull.eu>
Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
Reported-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Tested-by: Conor Dooley <conor.dooley@microchip.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Andy Chiu <andy.chiu@sifive.com>
Link: https://lore.kernel.org/r/20230403065207.1070974-1-bjorn@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
arch/riscv/kernel/traps.c

index 1f4e37be7eb388127de8397a89c51c5c42f34098..8c258b78c925c21e1814d5704428d30085a1e70a 100644 (file)
@@ -270,11 +270,11 @@ asmlinkage __visible __trap_section void do_trap_ecall_u(struct pt_regs *regs)
        if (user_mode(regs)) {
                ulong syscall = regs->a7;
 
-               syscall = syscall_enter_from_user_mode(regs, syscall);
-
                regs->epc += 4;
                regs->orig_a0 = regs->a0;
 
+               syscall = syscall_enter_from_user_mode(regs, syscall);
+
                if (syscall < NR_syscalls)
                        syscall_handler(regs, syscall);
                else