[PATCH v5] riscv: entry: set a0 = -ENOSYS only when syscall != -1

[patchwork-bot+linux-riscv at kernel.org]

Hello:

This patch was applied to riscv/linux.git (fixes)
by Palmer Dabbelt <palmer at rivosinc.com>:

On Tue,  1 Aug 2023 22:15:16 +0800 you wrote:
> When we test seccomp with 6.4 kernel, we found errno has wrong value.
> If we deny NETLINK_AUDIT with EAFNOSUPPORT, after f0bddf50586d, we will
> get ENOSYS instead. We got same result with commit 9c2598d43510 ("riscv:
> entry: Save a0 prior syscall_enter_from_user_mode()").
> 
> After analysing code, we think that regs->a0 = -ENOSYS should only be
> executed when syscall != -1. In __seccomp_filter, when seccomp rejected
> this syscall with specified errno, they will set a0 to return number as
> syscall ABI, and then return -1. This return number is finally pass as
> return number of syscall_enter_from_user_mode, and then is compared with
> NR_syscalls after converted to ulong (so it will be ULONG_MAX). The
> condition syscall < NR_syscalls will always be false, so regs->a0 = -ENOSYS
> is always executed. It covered a0 set by seccomp, so we always get
> ENOSYS when match seccomp RET_ERRNO rule.
> 
> [...]

Here is the summary with links:
  - [v5] riscv: entry: set a0 = -ENOSYS only when syscall != -1
    https://git.kernel.org/riscv/c/52449c17bdd1

You are awesome, thank you!
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