powerpc: Don't negate error in syscall_set_return_value()

Currently the only caller of syscall_set_return_value() is seccomp
filter, which is not enabled on powerpc.

This means we have not noticed that our implementation of
syscall_set_return_value() negates error, even though the value passed
in is already negative.

So remove the negation in syscall_set_return_value(), and expect the
caller to do it like all other implementations do.

Also add a comment about the ccr handling.

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

diff --git a/arch/powerpc/include/asm/syscall.h b/arch/powerpc/include/asm/syscall.h
index c6239da..cabe901 100644 (file)
--- a/arch/powerpc/include/asm/syscall.h
+++ b/arch/powerpc/include/asm/syscall.h
@@ -44,9 +44,15 @@ static inline void syscall_set_return_value(struct task_struct *task,
                                            struct pt_regs *regs,
                                            int error, long val)
 {
+       /*
+        * In the general case it's not obvious that we must deal with CCR
+        * here, as the syscall exit path will also do that for us. However
+        * there are some places, eg. the signal code, which check ccr to
+        * decide if the value in r3 is actually an error.
+        */
        if (error) {
                regs->ccr |= 0x10000000L;
-               regs->gpr[3] = -error;
+               regs->gpr[3] = error;
        } else {
                regs->ccr &= ~0x10000000L;
                regs->gpr[3] = val;