On Mon, Jun 15, 2020 at 10:13 AM Christoph Hellwig [off-list ref] wrote:

On Mon, Jun 15, 2020 at 03:31:35PM +0200, Arnd Bergmann wrote:

quoted

quoted

 #ifdef CONFIG_COMPAT
-       if (unlikely(argv.is_compat)) {
+       if (in_compat_syscall()) {
+               const compat_uptr_t __user *compat_argv =
+                       compat_ptr((unsigned long)argv);
                compat_uptr_t compat;

-               if (get_user(compat, argv.ptr.compat + nr))
+               if (get_user(compat, compat_argv + nr))
                        return ERR_PTR(-EFAULT);

                return compat_ptr(compat);
        }
 #endif

I would expect that the "#ifdef CONFIG_COMPAT" can be removed
now, since compat_ptr() and in_compat_syscall() are now defined
unconditionally. I have not tried that though.

True, I'll give it a spin.

quoted

quoted

+/*
+ * x32 syscalls are listed in the same table as x86_64 ones, so we need to
+ * define compat syscalls that are exactly the same as the native version for
+ * the syscall table machinery to work.  Sigh..
+ */
+#ifdef CONFIG_X86_X32
 COMPAT_SYSCALL_DEFINE3(execve, const char __user *, filename,
-       const compat_uptr_t __user *, argv,
-       const compat_uptr_t __user *, envp)
+                      const char __user *const __user *, argv,
+                      const char __user *const __user *, envp)
 {
-       return do_compat_execve(AT_FDCWD, getname(filename), argv, envp, 0);
+       return do_execveat(AT_FDCWD, getname(filename), argv, envp, 0, NULL);
 }

Maybe move it to arch/x86/kernel/process_64.c or arch/x86/entry/syscall_x32.c
to keep it out of the common code if this is needed.

I'd rather keep it in common code as that allows all the low-level
exec stuff to be marked static, and avoid us growing new pointless
compat variants through copy and paste.
smart compiler to d

quoted

I don't really understand
the comment, why can't this just use this?

That errors out with:

ld: arch/x86/entry/syscall_x32.o:(.rodata+0x1040): undefined reference to
`__x32_sys_execve'
ld: arch/x86/entry/syscall_x32.o:(.rodata+0x1108): undefined reference to
`__x32_sys_execveat'
make: *** [Makefile:1139: vmlinux] Error 1

I think I have a fix for this, by modifying the syscall wrappers to
add an alias for the __x32 variant to the native __x64_sys_foo().
I'll get back to you with a patch.

--
Brian Gerst

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