[PATCH v2 1/6] riscv: Implement syscall wrappers

Sami Tolvanen
2023-07-10T18:35:50Z

Commit f0bddf50586d ("riscv: entry: Convert to generic entry") moved
syscall handling to C code, which exposed function pointer type
mismatches that trip fine-grained forward-edge Control-Flow Integrity
(CFI) checks as syscall handlers are all called through the same
syscall_t pointer type. To fix the type mismatches, implement pt_regs
based syscall wrappers similarly to x86 and arm64.

This patch is based on arm64 syscall wrappers added in commit
4378a7d4be30 ("arm64: implement syscall wrappers"), where the main goal
was to minimize the risk of userspace-controlled values being used
under speculation. This may be a concern for riscv in future as well.

Following other architectures, the syscall wrappers generate three
functions for each syscall; __riscv_<compat_>sys_<name> takes a pt_regs
pointer and extracts arguments from registers, __se_<compat_>sys_<name>
is a sign-extension wrapper that casts the long arguments to the
correct types for the real syscall implementation, which is named
__do_<compat_>sys_<name>.

Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---
arch/riscv/Kconfig | 1 +
arch/riscv/include/asm/syscall.h | 5 +-
arch/riscv/include/asm/syscall_wrapper.h | 87 ++++++++++++++++++++++++
arch/riscv/kernel/compat_syscall_table.c | 8 ++-
arch/riscv/kernel/sys_riscv.c | 6 ++
arch/riscv/kernel/syscall_table.c | 8 ++-
6 files changed, 108 insertions(+), 7 deletions(-)
create mode 100644 arch/riscv/include/asm/syscall_wrapper.h

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 4c07b9189c86..a475ef1a0c1c 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -35,6 +35,7 @@ config RISCV
select ARCH_HAS_SET_MEMORY if MMU
select ARCH_HAS_STRICT_KERNEL_RWX if MMU && !XIP_KERNEL
select ARCH_HAS_STRICT_MODULE_RWX if MMU && !XIP_KERNEL
+ select ARCH_HAS_SYSCALL_WRAPPER
select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
select ARCH_HAS_UBSAN_SANITIZE_ALL
select ARCH_HAS_VDSO_DATA
diff --git a/arch/riscv/include/asm/syscall.h b/arch/riscv/include/asm/syscall.h
index 0148c6bd9675..121fff429dce 100644
--- a/arch/riscv/include/asm/syscall.h
+++ b/arch/riscv/include/asm/syscall.h
@@ -75,7 +75,7 @@ static inline int syscall_get_arch(struct task_struct *task)
#endif
}

-typedef long (*syscall_t)(ulong, ulong, ulong, ulong, ulong, ulong, ulong);
+typedef long (*syscall_t)(const struct pt_regs *);
static inline void syscall_handler(struct pt_regs *regs, ulong syscall)
{
syscall_t fn;
@@ -87,8 +87,7 @@ static inline void syscall_handler(struct pt_regs *regs, ulong syscall)
#endif
fn = sys_call_table[syscall];

- regs->a0 = fn(regs->orig_a0, regs->a1, regs->a2,
- regs->a3, regs->a4, regs->a5, regs->a6);
+ regs->a0 = fn(regs);
}

static inline bool arch_syscall_is_vdso_sigreturn(struct pt_regs *regs)
diff --git a/arch/riscv/include/asm/syscall_wrapper.h b/arch/riscv/include/asm/syscall_wrapper.h
new file mode 100644
index 000000000000..1d7942c8a6cb
--- /dev/null
+++ b/arch/riscv/include/asm/syscall_wrapper.h
@@ -0,0 +1,87 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * syscall_wrapper.h - riscv specific wrappers to syscall definitions
+ *
+ * Based on arch/arm64/include/syscall_wrapper.h
+ */
+
+#ifndef __ASM_SYSCALL_WRAPPER_H
+#define __ASM_SYSCALL_WRAPPER_H
+
+#include <asm/ptrace.h>
+
+asmlinkage long __riscv_sys_ni_syscall(const struct pt_regs *);
+
+#define SC_RISCV_REGS_TO_ARGS(x, ...) \
+ __MAP(x,__SC_ARGS \
+ ,,regs->orig_a0,,regs->a1,,regs->a2 \
+ ,,regs->a3,,regs->a4,,regs->a5,,regs->a6)
+
+#ifdef CONFIG_COMPAT
+
+#define COMPAT_SYSCALL_DEFINEx(x, name, ...) \
+ asmlinkage long __riscv_compat_sys##name(const struct pt_regs *regs); \
+ ALLOW_ERROR_INJECTION(__riscv_compat_sys##name, ERRNO); \
+ static long __se_compat_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)); \
+ static inline long __do_compat_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__)); \
+ asmlinkage long __riscv_compat_sys##name(const struct pt_regs *regs) \
+ { \
+ return __se_compat_sys##name(SC_RISCV_REGS_TO_ARGS(x,__VA_ARGS__)); \
+ } \
+ static long __se_compat_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)) \
+ { \
+ return __do_compat_sys##name(__MAP(x,__SC_DELOUSE,__VA_ARGS__)); \
+ } \
+ static inline long __do_compat_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))
+
+#define COMPAT_SYSCALL_DEFINE0(sname) \
+ asmlinkage long __riscv_compat_sys_##sname(const struct pt_regs *__unused); \
+ ALLOW_ERROR_INJECTION(__riscv_compat_sys_##sname, ERRNO); \
+ asmlinkage long __riscv_compat_sys_##sname(const struct pt_regs *__unused)
+
+#define COND_SYSCALL_COMPAT(name) \
+ asmlinkage long __weak __riscv_compat_sys_##name(const struct pt_regs *regs); \
+ asmlinkage long __weak __riscv_compat_sys_##name(const struct pt_regs *regs) \
+ { \
+ return sys_ni_syscall(); \
+ }
+
+#define COMPAT_SYS_NI(name) \
+ SYSCALL_ALIAS(__riscv_compat_sys_##name, sys_ni_posix_timers);
+
+#endif /* CONFIG_COMPAT */
+
+#define __SYSCALL_DEFINEx(x, name, ...) \
+ asmlinkage long __riscv_sys##name(const struct pt_regs *regs); \
+ ALLOW_ERROR_INJECTION(__riscv_sys##name, ERRNO); \
+ static long __se_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)); \
+ static inline long __do_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__)); \
+ asmlinkage long __riscv_sys##name(const struct pt_regs *regs) \
+ { \
+ return __se_sys##name(SC_RISCV_REGS_TO_ARGS(x,__VA_ARGS__)); \
+ } \
+ static long __se_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)) \
+ { \
+ long ret = __do_sys##name(__MAP(x,__SC_CAST,__VA_ARGS__)); \
+ __MAP(x,__SC_TEST,__VA_ARGS__); \
+ __PROTECT(x, ret,__MAP(x,__SC_ARGS,__VA_ARGS__)); \
+ return ret; \
+ } \
+ static inline long __do_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))
+
+#define SYSCALL_DEFINE0(sname) \
+ SYSCALL_METADATA(_##sname, 0); \
+ asmlinkage long __riscv_sys_##sname(const struct pt_regs *__unused); \
+ ALLOW_ERROR_INJECTION(__riscv_sys_##sname, ERRNO); \
+ asmlinkage long __riscv_sys_##sname(const struct pt_regs *__unused)
+
+#define COND_SYSCALL(name) \
+ asmlinkage long __weak __riscv_sys_##name(const struct pt_regs *regs); \
+ asmlinkage long __weak __riscv_sys_##name(const struct pt_regs *regs) \
+ { \
+ return sys_ni_syscall(); \
+ }
+
+#define SYS_NI(name) SYSCALL_ALIAS(__riscv_sys_##name, sys_ni_posix_timers);
+
+#endif /* __ASM_SYSCALL_WRAPPER_H */
diff --git a/arch/riscv/kernel/compat_syscall_table.c b/arch/riscv/kernel/compat_syscall_table.c
index 651f2b009c28..ad7f2d712f5f 100644
--- a/arch/riscv/kernel/compat_syscall_table.c
+++ b/arch/riscv/kernel/compat_syscall_table.c
@@ -9,11 +9,15 @@
#include <asm/syscall.h>

#undef __SYSCALL
-#define __SYSCALL(nr, call) [nr] = (call),
+#define __SYSCALL(nr, call) asmlinkage long __riscv_##call(const struct pt_regs *);
+#include <asm/unistd.h>
+
+#undef __SYSCALL
+#define __SYSCALL(nr, call) [nr] = __riscv_##call,

asmlinkage long compat_sys_rt_sigreturn(void);

void * const compat_sys_call_table[__NR_syscalls] = {
- [0 ... __NR_syscalls - 1] = sys_ni_syscall,
+ [0 ... __NR_syscalls - 1] = __riscv_sys_ni_syscall,
#include <asm/unistd.h>
};
diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c
index 26ef5526bfb4..473159b5f303 100644
--- a/arch/riscv/kernel/sys_riscv.c
+++ b/arch/riscv/kernel/sys_riscv.c
@@ -335,3 +335,9 @@ SYSCALL_DEFINE5(riscv_hwprobe, struct riscv_hwprobe __user *, pairs,
return do_riscv_hwprobe(pairs, pair_count, cpu_count,
cpus, flags);
}
+
+/* Not defined using SYSCALL_DEFINE0 to avoid error injection */
+asmlinkage long __riscv_sys_ni_syscall(const struct pt_regs *__unused)
+{
+ return -ENOSYS;
+}
diff --git a/arch/riscv/kernel/syscall_table.c b/arch/riscv/kernel/syscall_table.c
index 44b1420a2270..dda913764903 100644
--- a/arch/riscv/kernel/syscall_table.c
+++ b/arch/riscv/kernel/syscall_table.c
@@ -10,9 +10,13 @@
#include <asm/syscall.h>

#undef __SYSCALL
-#define __SYSCALL(nr, call) [nr] = (call),
+#define __SYSCALL(nr, call) asmlinkage long __riscv_##call(const struct pt_regs *);
+#include <asm/unistd.h>
+
+#undef __SYSCALL
+#define __SYSCALL(nr, call) [nr] = __riscv_##call,

void * const sys_call_table[__NR_syscalls] = {
- [0 ... __NR_syscalls - 1] = sys_ni_syscall,
+ [0 ... __NR_syscalls - 1] = __riscv_sys_ni_syscall,
#include <asm/unistd.h>
};
--
2.41.0.255.g8b1d071c50-goog