On Fri, Jan 10, 2025 at 08:37:46AM +0100, Sven Schnelle wrote:
"Dmitry V. Levin" <ldv@xxxxxxxxx> writes:
Similar to syscall_set_arguments() that complements
syscall_get_arguments(), introduce syscall_set_nr()
that complements syscall_get_nr().
syscall_set_nr() is going to be needed along with
syscall_set_arguments() on all HAVE_ARCH_TRACEHOOK
architectures to implement PTRACE_SET_SYSCALL_INFO API.
[...]
diff --git a/arch/s390/include/asm/syscall.h b/arch/s390/include/asm/syscall.h
index b3dd883699e7..1c0e349fd5c9 100644
--- a/arch/s390/include/asm/syscall.h
+++ b/arch/s390/include/asm/syscall.h
@@ -24,6 +24,13 @@ static inline long syscall_get_nr(struct task_struct *task,
(regs->int_code & 0xffff) : -1;
}
+static inline void syscall_set_nr(struct task_struct *task,
+ struct pt_regs *regs,
+ int nr)
+{
I think there should be a
if (!test_pt_regs_flags(regs, PIF_SYSCALL))
return;
before the modification so a user can't accidentally change int_code
when ptrace stopped in a non-syscall path.
The reason why syscall_get_nr() has this check on s390 (and similar checks
on arc, powerpc, and sparc) is that syscall_get_nr() can be called while
the target task is not in syscall.
Unlike syscall_get_nr(), syscall_set_nr() can be called only when the
target task is stopped for tracing on entering syscall: the description in
include/asm-generic/syscall.h explicitly states that, and the follow-up
patch that introduces PTRACE_SET_SYSCALL_INFO adds a syscall_set_nr() call
when the tracee is stopped on entering syscall in either
PTRACE_SYSCALL_INFO_ENTRY or PTRACE_SYSCALL_INFO_SECCOMP state.
I don't mind adding a check, but syscall_set_nr() invocation while the
target task is not in syscall wouldn't be a result of user actions but
a kernel programing error, and in that case WARN_ON_ONCE() would be more
appropriate.
If calling syscall_set_nr() while the target task is not in syscall was
legal, then syscall_set_nr() would have been designed to return a value
indicating the status of operation.
Anyway, I'll add an explanatory comment to syscall_set_nr() on all
architectures where syscall_get_nr() has a check.
--
ldv
