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When we test seccomp with 6.4 kernel, we found errno has wrong value. If we deny NETLINK_AUDIT with EAFNOSUPPORT, afterf0bddf5058, we will get ENOSYS instead. We got same result with commit9c2598d435("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:f0bddf5058("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> Tested-by: Emil Renner Berthing <emil.renner.berthing@canonical.com> Reviewed-by: Björn Töpel <bjorn@rivosinc.com> Reviewed-by: Guo Ren <guoren@kernel.org> Link: https://lore.kernel.org/r/20230801141607.435192-1-CoelacanthusHex@gmail.com Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.