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The uname(3) syscall is utilized by zlib-ng on RISC-V to decide whether the kernel handles VILL bit of V extension properly (by checking the kernel version against 6.5). Allow it in the seccomp sandbox. Signed-off-by: Icenowy Zheng <uwu@icenowy.me>
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Previously, RVV/Zbc is used when - Linux kernel version (detected by uname(2)) is greater or equal to 6.5, and HWCAP claims support for such extension, or - Linux kernel version is less than 6.5, but compiler claims support for the extension and for RVV, we additionally check whether it's (the earlier, draft) v0.7.1 release or the (the later, ratified) v1.0 release. Zlib-ng only supports v1.0. This strategy is problematic in several aspects, - Fallback to compile-time constants with Linux kernel earlier than 6.5 makes it hard for distributions to ship the same binary for different machines with different kernel versions. - Detecting Linux kernel version through uname(2) could violate sandbox enforcement[1]. And since RVV introduces special vector registers, RVV usage in userspace relies on the kernel to implement proper context switching, which is only present since Linux kernel 6.5, which is also the version when COMPAT_HWCAP_ISA_V was introduced. This makes it reasonable to only do HWCAP-based extension detection for RVV. The additional check for RVV version is also unnecessary since in mainline Linux kernel, COMPAT_HWCAP_ISA_V is only set when a ratified v1.0 implementation of RVV is present. A downstream kernel claiming COMPAT_HWCAP_ISA_V with a v0.7.1 RVV implementation breaks the kABI, and userspace shouldn't pay for the mistake. This patch removes extra detection logic, now RVV is and only is used when the kernel claims COMPAT_HWCAP_ISA_V. The detection logic of Zbc checks an undefined HWCAP bit, thus doesn't detect Zbc correctly with any current Linux kernel, which should be fixed with another patch. Fixes: 6ff8b52 ("Support RVV hwcap detect at runtime") Link: openssh/openssh-portable#605 # [1] Closes: zlib-ng#1705 Closes: zlib-ng#1769 Signed-off-by: Yao Zi <ziyao@disroot.org>
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Merged as ec41739 - thanks |
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The uname(3) syscall is utilized by zlib-ng on RISC-V to decide whether the kernel handles VILL bit of V extension properly (by checking the kernel version against 6.5).
Allow it in the seccomp sandbox.