From: Celeste Liu <coelacanthushex@gmail.com>
To: "Palmer Dabbelt" <palmer@rivosinc.com>,
"Paul Walmsley" <paul.walmsley@sifive.com>,
"Albert Ou" <aou@eecs.berkeley.edu>,
"Guo Ren" <guoren@kernel.org>, "Björn Töpel" <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: [PATCH v2] riscv: entry: set a0 prior to syscall_enter_from_user_mode
Date: Wed, 19 Jul 2023 00:28:46 +0800 [thread overview]
Message-ID: <20230718162940.226118-1-CoelacanthusHex@gmail.com> (raw)
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 9c2598d43510 ("riscv: entry: Save a0
prior syscall_enter_from_user_mode()").
After analysing code, we think that regs->a0 = -ENOSYS should be advanced before
syscall_enter_from_user_mode to fix this problem. 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 executable. 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>
---
v1 -> v2: added explanation on why always got ENOSYS
arch/riscv/kernel/traps.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
index f910dfccbf5d2..ccadb5ffd063c 100644
--- a/arch/riscv/kernel/traps.c
+++ b/arch/riscv/kernel/traps.c
@@ -301,6 +301,7 @@ 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);
@@ -308,8 +309,6 @@ asmlinkage __visible __trap_section void do_trap_ecall_u(struct pt_regs *regs)
if (syscall < NR_syscalls)
syscall_handler(regs, syscall);
- else
- regs->a0 = -ENOSYS;
syscall_exit_to_user_mode(regs);
} else {
--
2.41.0
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next reply other threads:[~2023-07-19 6:57 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-18 16:28 Celeste Liu [this message]
2023-07-18 19:35 ` [PATCH v2] riscv: entry: set a0 prior to syscall_enter_from_user_mode Björn Töpel
2023-07-18 20:35 ` Celeste Liu
2023-07-18 20:48 ` Celeste Liu
2023-07-18 20:50 ` Björn Töpel
2023-07-18 20:56 ` Celeste Liu
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