[PATCH 2/2] riscv: fix syscall_{get,set}_arguments

[David Abdurachmanov <david.abdurachmanov@gmail.com>]

Testing with libseccomp master branch revealed that testcases with
filters on syscall arguments were failing due to wrong values. Seccomp
uses syscall_get_argumentsi() to copy syscall arguments, and there is a
bug in pointer arithmetics in memcpy() call.

Two alternative implementation were tested: the one in this patch and
another one based on while-break loop. Both delivered the same results.

This implementation is also used in arm, arm64 and nds32 arches.

Signed-off-by: David Abdurachmanov <david.abdurachmanov@gmail.com>
---
 arch/riscv/include/asm/syscall.h | 42 ++++++++++++++++++++++++--------
 1 file changed, 32 insertions(+), 10 deletions(-)

diff --git a/arch/riscv/include/asm/syscall.h b/arch/riscv/include/asm/syscall.h
index bba3da6ef157..26ceb434a433 100644
--- a/arch/riscv/include/asm/syscall.h
+++ b/arch/riscv/include/asm/syscall.h
@@ -70,19 +70,32 @@ static inline void syscall_set_return_value(struct task_struct *task,
 	regs->a0 = (long) error ?: val;
 }
 
+#define SYSCALL_MAX_ARGS 6
+
 static inline void syscall_get_arguments(struct task_struct *task,
 					 struct pt_regs *regs,
 					 unsigned int i, unsigned int n,
 					 unsigned long *args)
 {
-	BUG_ON(i + n > 6);
+	if (n == 0)
+		return;
+
+	if (i + n > SYSCALL_MAX_ARGS) {
+		unsigned long *args_bad = args + SYSCALL_MAX_ARGS - i;
+		unsigned int n_bad = n + i - SYSCALL_MAX_ARGS;
+		pr_warning("%s called with max args %d, handling only %d\n",
+			__func__, i + n, SYSCALL_MAX_ARGS);
+		memset(args_bad, 0, n_bad * sizeof(args[0]));
+	}
+
 	if (i == 0) {
 		args[0] = regs->orig_a0;
 		args++;
 		i++;
 		n--;
 	}
-	memcpy(args, &regs->a1 + i * sizeof(regs->a1), n * sizeof(args[0]));
+
+	memcpy(args, &regs->a0 + i, n * sizeof(args[0]));
 }
 
 static inline void syscall_set_arguments(struct task_struct *task,
@@ -90,14 +103,23 @@ static inline void syscall_set_arguments(struct task_struct *task,
 					 unsigned int i, unsigned int n,
 					 const unsigned long *args)
 {
-	BUG_ON(i + n > 6);
-        if (i == 0) {
-                regs->orig_a0 = args[0];
-                args++;
-                i++;
-                n--;
-        }
-	memcpy(&regs->a1 + i * sizeof(regs->a1), args, n * sizeof(regs->a0));
+	if (n == 0)
+		return;
+
+	if (i + n > SYSCALL_MAX_ARGS) {
+		pr_warning("%s called with max args %d, handling only %d\n",
+			__func__, i + n, SYSCALL_MAX_ARGS);
+		n = SYSCALL_MAX_ARGS - i;
+	}
+
+	if (i == 0) {
+		regs->orig_a0 = args[0];
+		args++;
+		i++;
+		n--;
+	}
+
+	memcpy(&regs->a0 + i, args, n * sizeof(args[0]));
 }
 
 static inline int syscall_get_arch(void)
-- 
2.19.2


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