[PATCH v8 2/7] um: use execveat to create userspace MMs

[Tiwei Bie]

On 2024/7/5 03:05, Benjamin Berg wrote:
[...]
>  static int userspace_tramp(void *stack)
>  {
> -	struct sigaction sa;
> -	void *addr;
> -	int fd;
> +	char *const argv[] = { "uml-userspace", NULL };
> +	int pipe_fds[2];
>  	unsigned long long offset;
> -	unsigned long segv_handler = STUB_CODE +
> -				     (unsigned long) stub_segv_handler -
> -				     (unsigned long) __syscall_stub_start;
> -
> -	ptrace(PTRACE_TRACEME, 0, 0, 0);
> -
> -	signal(SIGTERM, SIG_DFL);
> -	signal(SIGWINCH, SIG_IGN);
> -
> -	fd = phys_mapping(uml_to_phys(__syscall_stub_start), &offset);
> -	addr = mmap64((void *) STUB_CODE, UM_KERN_PAGE_SIZE,
> -		      PROT_EXEC, MAP_FIXED | MAP_PRIVATE, fd, offset);
> -	if (addr == MAP_FAILED) {
> -		os_info("mapping mmap stub at 0x%lx failed, errno = %d\n",
> -			STUB_CODE, errno);
> -		exit(1);
> +	struct stub_init_data init_data = {
> +		.stub_start = STUB_START,
> +		.segv_handler = STUB_CODE +
> +				(unsigned long) stub_segv_handler -
> +				(unsigned long) __syscall_stub_start,
> +	};
> +	struct iomem_region *iomem;
> +	int ret;
> +
> +	init_data.stub_code_fd = phys_mapping(uml_to_phys(__syscall_stub_start),
> +					      &offset);
> +	init_data.stub_code_offset = MMAP_OFFSET(offset);
> +
> +	init_data.stub_data_fd = phys_mapping(uml_to_phys(stack), &offset);
> +	init_data.stub_data_offset = MMAP_OFFSET(offset);
> +
> +	/* Set CLOEXEC on all FDs and then unset on all memory related FDs */
> +	close_range(0, ~0U, CLOSE_RANGE_CLOEXEC);

I got a link error on Ubuntu 22.04.4 (glibc-2.35) when STATIC_LINK is enabled:

/usr/bin/ld:
/usr/lib/gcc/x86_64-linux-gnu/11/../../../x86_64-linux-gnu/libc.a(close_range.o):
in function `__close_range':
(.text+0x0): multiple definition of `__close_range';
fs/file.o:/home/test/linux/fs/file.c:741: first defined here

We probably need something like this:

diff --git a/arch/um/Makefile b/arch/um/Makefile
index 00b63bac5eff..31e367e8ab4d 100644
--- a/arch/um/Makefile
+++ b/arch/um/Makefile
@@ -61,7 +61,8 @@ KBUILD_CFLAGS += $(CFLAGS) $(CFLAGS-y) -D__arch_um__ \
 	$(ARCH_INCLUDE) $(MODE_INCLUDE) -Dvmap=kernel_vmap	\
 	-Dlongjmp=kernel_longjmp -Dsetjmp=kernel_setjmp \
 	-Din6addr_loopback=kernel_in6addr_loopback \
-	-Din6addr_any=kernel_in6addr_any -Dstrrchr=kernel_strrchr
+	-Din6addr_any=kernel_in6addr_any -Dstrrchr=kernel_strrchr \
+	-D__close_range=kernel__close_range

 KBUILD_RUSTFLAGS += -Crelocation-model=pie

Regards,
Tiwei