parisc: Fix ptrace syscall number and return value modification (98e8b6c9) · Commits · 戴 / test

Mike Frysinger reported that his ptrace testcase showed strange behaviour on parisc: It was not possible to avoid a syscall and the return value of a syscall couldn't be changed. To modify a syscall number, we were missing to save the new syscall number to gr20 which is then picked up later in assembly again. The effect that the return value couldn't be changed is a side-effect of another bug in the assembly code. When a process is ptraced, userspace expects each syscall to report entrance and exit of a syscall. If a syscall number was given which doesn't exist, we jumped to the normal syscall exit code instead of informing userspace that the (non-existant) syscall exits. This unexpected behaviour confuses userspace and thus the bug was misinterpreted as if we can't change the return value. This patch fixes both problems and was tested on 64bit kernel with 32bit userspace. Signed-off-by:

Helge Deller <deller@gmx.de> Cc: Mike Frysinger <vapier@gentoo.org> Cc: stable@vger.kernel.org # v4.0+ Tested-by:

Mike Frysinger <vapier@gentoo.org>

arch/parisc/kernel/ptrace.c

+11 −5

Original line number	Diff line number	Diff line
		@@ -269,14 +269,19 @@ long compat_arch_ptrace(struct task_struct *child, compat_long_t request,

		long do_syscall_trace_enter(struct pt_regs *regs)
		{
		long ret = 0;

		/* Do the secure computing check first. */
		secure_computing_strict(regs->gr[20]);

		if (test_thread_flag(TIF_SYSCALL_TRACE) &&
		tracehook_report_syscall_entry(regs))
		ret = -1L;
		tracehook_report_syscall_entry(regs)) {
		/*
		* Tracing decided this syscall should not happen or the
		* debugger stored an invalid system call number. Skip
		* the system call and the system call restart handling.
		*/
		regs->gr[20] = -1UL;
		goto out;
		}

		#ifdef CONFIG_64BIT
		if (!is_compat_task())
		@@ -290,7 +295,8 @@ long do_syscall_trace_enter(struct pt_regs *regs)
		regs->gr[24] & 0xffffffff,
		regs->gr[23] & 0xffffffff);

		return ret ? : regs->gr[20];
		out:
		return regs->gr[20];
		}

		void do_syscall_trace_exit(struct pt_regs *regs)

arch/parisc/kernel/syscall.S

+4 −1

Original line number	Diff line number	Diff line
		@@ -343,7 +343,7 @@ tracesys_next:
		#endif

		comiclr,>>= __NR_Linux_syscalls, %r20, %r0
		b,n .Lsyscall_nosys
		b,n .Ltracesys_nosys

		LDREGX %r20(%r19), %r19

		@@ -359,6 +359,9 @@ tracesys_next:
		be 0(%sr7,%r19)
		ldo R%tracesys_exit(%r2),%r2

		.Ltracesys_nosys:
		ldo -ENOSYS(%r0),%r28 /* set errno */

		/* Do not call this function on the gateway page, because it
		makes a direct call to syscall_trace. */

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