https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=273929
Bug ID: 273929
Summary: AArch64 machine-dependent code clobbers X0 in SIGTRAP
from capsicum violations
Product: Base System
Version: CURRENT
Hardware: arm64
OS: Any
Status: New
Severity: Affects Only Me
Priority: ---
Component: kern
Assignee: b...@freebsd.org
Reporter: thera...@freebsd.org
X0 is used as both the first argument register and as the return value. If
SIGTRAP is delivered to a process for a Capsicum violation, the mcontext_t in
the signal should contain the arguments so that software can trap and emulate
the system calls. This works on x86[-64] but on AArch64 X0 is overwritten
before the system call handler is entered. When emulating `open`, for example,
the signal frame always sees the path as `(char*)94`, which makes this
impossible.
It would be nice if this could be fixed before 14.0 or be subject to an EN
afterwards, since it makes capsicum trap-and-emulate behaviour unusable
currently.
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