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Message-ID: <20230720140348.4716-1-CoelacanthusHex@gmail.com>
Date: Thu, 20 Jul 2023 21:56:29 +0800
From: Celeste Liu <coelacanthushex@...il.com>
To: Palmer Dabbelt <palmer@...osinc.com>,
Paul Walmsley <paul.walmsley@...ive.com>,
Albert Ou <aou@...s.berkeley.edu>, Guo Ren <guoren@...nel.org>,
Björn Töpel <bjorn@...osinc.com>,
Conor Dooley <conor.dooley@...rochip.com>,
linux-riscv@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org, Andreas Schwab <schwab@...e.de>,
David Laight <David.Laight@...LAB.COM>,
Celeste Liu <CoelacanthusHex@...il.com>,
Felix Yan <felixonmars@...hlinux.org>,
Ruizhe Pan <c141028@...il.com>,
Shiqi Zhang <shiqi@...c.iscas.ac.cn>
Subject: [PATCH v4] riscv: entry: set a0 = -ENOSYS only when syscall != -1
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.
Fixes: f0bddf50586d ("riscv: entry: Convert to generic entry")
Reported-by: Felix Yan <felixonmars@...hlinux.org>
Co-developed-by: Ruizhe Pan <c141028@...il.com>
Signed-off-by: Ruizhe Pan <c141028@...il.com>
Co-developed-by: Shiqi Zhang <shiqi@...c.iscas.ac.cn>
Signed-off-by: Shiqi Zhang <shiqi@...c.iscas.ac.cn>
Signed-off-by: Celeste Liu <CoelacanthusHex@...il.com>
Tested-by: Felix Yan <felixonmars@...hlinux.org>
Reviewed-by: Björn Töpel <bjorn@...osinc.com>
Reviewed-by: Guo Ren <guoren@...nel.org>
---
v3 -> v4: use long instead of ulong to reduce type cast and avoid
implementation-defined behavior, and make the judgment of syscall
invalid more explicit
v2 -> v3: use if-statement instead of set default value,
clarify the type of syscall
v1 -> v2: added explanation on why always got ENOSYS
arch/riscv/kernel/traps.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
index f910dfccbf5d2..729f79c97e2bf 100644
--- a/arch/riscv/kernel/traps.c
+++ b/arch/riscv/kernel/traps.c
@@ -297,7 +297,7 @@ asmlinkage __visible __trap_section void do_trap_break(struct pt_regs *regs)
asmlinkage __visible __trap_section void do_trap_ecall_u(struct pt_regs *regs)
{
if (user_mode(regs)) {
- ulong syscall = regs->a7;
+ long syscall = regs->a7;
regs->epc += 4;
regs->orig_a0 = regs->a0;
@@ -306,9 +306,9 @@ asmlinkage __visible __trap_section void do_trap_ecall_u(struct pt_regs *regs)
syscall = syscall_enter_from_user_mode(regs, syscall);
- if (syscall < NR_syscalls)
+ if (syscall >= 0 && syscall < NR_syscalls)
syscall_handler(regs, syscall);
- else
+ else if (syscall != -1)
regs->a0 = -ENOSYS;
syscall_exit_to_user_mode(regs);
--
2.41.0
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