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