[PATCH 3/6 v3] riscv: Fix syscall_get_arguments() and syscall_set_arguments()

[Steven Rostedt]

From: "Dmitry V. Levin" <l...@altlinux.org>

RISC-V syscall arguments are located in orig_a0,a1..a5 fields
of struct pt_regs.

Due to an off-by-one bug and a bug in pointer arithmetic
syscall_get_arguments() was reading s3..s7 fields instead of a1..a5.
Likewise, syscall_set_arguments() was writing s3..s7 fields
instead of a1..a5.

Link: http://lkml.kernel.org/r/20190329171221.ga32...@altlinux.org

Fixes: e2c0cdfba7f69 ("RISC-V: User-facing API")
Cc: Ingo Molnar <mi...@redhat.com>
Cc: Kees Cook <keesc...@chromium.org>
Cc: Andy Lutomirski <l...@amacapital.net>
Cc: Will Drewry <w...@chromium.org>
Cc: Palmer Dabbelt <pal...@sifive.com>
Cc: Albert Ou <a...@eecs.berkeley.edu>
Cc: linux-ri...@lists.infradead.org
Cc: sta...@vger.kernel.org # v4.15+
Signed-off-by: Dmitry V. Levin <l...@altlinux.org>
Signed-off-by: Steven Rostedt (VMware) <rost...@goodmis.org>
---
 arch/riscv/include/asm/syscall.h | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/riscv/include/asm/syscall.h b/arch/riscv/include/asm/syscall.h
index bba3da6ef157..6ea9e1804233 100644
--- a/arch/riscv/include/asm/syscall.h
+++ b/arch/riscv/include/asm/syscall.h
@@ -79,10 +79,11 @@ static inline void syscall_get_arguments(struct task_struct 
*task,
        if (i == 0) {
                args[0] = regs->orig_a0;
                args++;
-               i++;
                n--;
+       } else {
+               i--;
        }
-       memcpy(args, &regs->a1 + i * sizeof(regs->a1), n * sizeof(args[0]));
+       memcpy(args, &regs->a1 + i, n * sizeof(args[0]));
 }
 
 static inline void syscall_set_arguments(struct task_struct *task,
@@ -94,10 +95,11 @@ static inline void syscall_set_arguments(struct task_struct 
*task,
         if (i == 0) {
                 regs->orig_a0 = args[0];
                 args++;
-                i++;
                 n--;
-        }
-       memcpy(&regs->a1 + i * sizeof(regs->a1), args, n * sizeof(regs->a0));
+       } else {
+               i--;
+       }
+       memcpy(&regs->a1 + i, args, n * sizeof(regs->a1));
 }
 
 static inline int syscall_get_arch(void)
-- 
2.20.1