Commit 1cb9839b authored Jul 23, 2015 by Michael Ellerman

powerpc: Use orig_gpr3 in syscall_get_arguments()



Currently syscall_get_arguments() is used by syscall tracepoints, and
collect_syscall() which is used in some debugging as well as
/proc/pid/syscall.

The current implementation just copies regs->gpr[3 .. 5] out, which is
fine for all the current use cases.

When we enable seccomp filter, that will also start using
syscall_get_arguments(). However for seccomp filter we want to use r3
as the return value of the syscall, and orig_gpr3 as the first
parameter. This will allow seccomp to modify the return value in r3.

To support this we need to modify syscall_get_arguments() to return
orig_gpr3 instead of r3. This is safe for all uses because orig_gpr3
always contains the r3 value that was passed to the syscall. We store it
in the syscall entry path and never modify it.

Update syscall_set_arguments() while we're here, even though it's never
used.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Kees Cook <keescook@chromium.org>

parent a7657844

arch/powerpc/include/asm/syscall.h

+13 −3

Original line number	Diff line number	Diff line
		@@ -64,7 +64,7 @@ static inline void syscall_get_arguments(struct task_struct *task,
		unsigned int i, unsigned int n,
		unsigned long *args)
		{
		unsigned long mask = -1UL;
		unsigned long val, mask = -1UL;

		BUG_ON(i + n > 6);

		@@ -72,8 +72,14 @@ static inline void syscall_get_arguments(struct task_struct *task,
		if (test_tsk_thread_flag(task, TIF_32BIT))
		mask = 0xffffffff;
		#endif
		while (n--)
		args[n] = regs->gpr[3 + i + n] & mask;
		while (n--) {
		if (n == 0 && i == 0)
		val = regs->orig_gpr3;
		else
		val = regs->gpr[3 + i + n];

		args[n] = val & mask;
		}
		}

		static inline void syscall_set_arguments(struct task_struct *task,
		@@ -83,6 +89,10 @@ static inline void syscall_set_arguments(struct task_struct *task,
		{
		BUG_ON(i + n > 6);
		memcpy(&regs->gpr[3 + i], args, n * sizeof(args[0]));

		/* Also copy the first argument into orig_gpr3 */
		if (i == 0 && n > 0)
		regs->orig_gpr3 = args[0];
		}

		static inline int syscall_get_arch(void)