[PATCH 1/6] riscv: Implement syscall wrappers

[Kees Cook]

On Thu, Jun 29, 2023 at 11:42:46PM +0000, Sami Tolvanen wrote:
> 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>.
> 
> Signed-off-by: Sami Tolvanen <samitolvanen at google.com>

This all looks correct to me; though I have not run tested it. I'm glad
to see another arch using this style.

Reviewed-by: Kees Cook <keescook at chromium.org>

-- 
Kees Cook