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From:   =?utf-8?B?QmrDtnJuIFTDtnBlbA==?= <bjorn@kernel.org>
To:     Celeste Liu <coelacanthushex@gmail.com>,
        Palmer Dabbelt <palmer@rivosinc.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Albert Ou <aou@eecs.berkeley.edu>, Guo Ren <guoren@kernel.org>,
        =?utf-8?B?QmrDtnJu?= =?utf-8?B?IFTDtnBlbA==?= 
        <bjorn@rivosinc.com>, Conor Dooley <conor.dooley@microchip.com>,
        linux-riscv@lists.infradead.org
Cc:     linux-kernel@vger.kernel.org,
        Celeste Liu <CoelacanthusHex@gmail.com>,
        Felix Yan <felixonmars@archlinux.org>,
        Ruizhe Pan <c141028@gmail.com>,
        Shiqi Zhang <shiqi@isrc.iscas.ac.cn>
Subject: Re: [PATCH v3] riscv: entry: set a0 = -ENOSYS only when syscall != -1
In-Reply-To: <20230718210037.250665-1-CoelacanthusHex@gmail.com>
References: <20230718210037.250665-1-CoelacanthusHex@gmail.com>
Date:   Tue, 18 Jul 2023 23:20:27 +0200
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Celeste Liu <coelacanthushex@gmail.com> writes:

> 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 =3D -ENOSYS should only be e=
xecuted
> when syscall !=3D -1 In __seccomp_filter, when seccomp rejected this sysc=
all with
> specified errno, they will set a0 to return number as syscall ABI, and th=
en
> 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 =3D -ENOSYS is al=
ways
> executed. It covered a0 set by seccomp, so we always get ENOSYS when match
> seccomp RET_ERRNO rule.
>
> Fixes: f0bddf50586d ("riscv: entry: Convert to generic entry")
> Reported-by: Felix Yan <felixonmars@archlinux.org>
> Co-developed-by: Ruizhe Pan <c141028@gmail.com>
> Signed-off-by: Ruizhe Pan <c141028@gmail.com>
> Co-developed-by: Shiqi Zhang <shiqi@isrc.iscas.ac.cn>
> Signed-off-by: Shiqi Zhang <shiqi@isrc.iscas.ac.cn>
> Signed-off-by: Celeste Liu <CoelacanthusHex@gmail.com>
> Tested-by: Felix Yan <felixonmars@archlinux.org>

Reviewed-by: Bj=C3=B6rn T=C3=B6pel <bjorn@rivosinc.com>