Re: [PATCH v15 17/17] selftests, arm64: add a selftest for passing tagged pointers to kernel

Andrey Konovalov
2019-05-31T14:22:02Z

On Wed, May 22, 2019 at 4:16 PM Catalin Marinas <catalin.marinas@arm.com> wrote:
>
> On Mon, May 06, 2019 at 06:31:03PM +0200, Andrey Konovalov wrote:
> > This patch is a part of a series that extends arm64 kernel ABI to allow to
> > pass tagged user pointers (with the top byte set to something else other
> > than 0x00) as syscall arguments.
> >
> > This patch adds a simple test, that calls the uname syscall with a
> > tagged user pointer as an argument. Without the kernel accepting tagged
> > user pointers the test fails with EFAULT.
>
> That's probably sufficient for a simple example. Something we could add
> to Documentation maybe is a small library that can be LD_PRELOAD'ed so
> that you can run a lot more tests like LTP.

Should I add this into this series, or should this go into Vincenzo's patchset?

>
> We could add this to selftests but I think it's too glibc specific.
>
> --------------------8<------------------------------------
> #include <stdlib.h>
>
> #define TAG_SHIFT (56)
> #define TAG_MASK (0xffUL << TAG_SHIFT)
>
> void *__libc_malloc(size_t size);
> void __libc_free(void *ptr);
> void *__libc_realloc(void *ptr, size_t size);
> void *__libc_calloc(size_t nmemb, size_t size);
>
> static void *tag_ptr(void *ptr)
> {
> unsigned long tag = rand() & 0xff;
> if (!ptr)
> return ptr;
> return (void *)((unsigned long)ptr | (tag << TAG_SHIFT));
> }
>
> static void *untag_ptr(void *ptr)
> {
> return (void *)((unsigned long)ptr & ~TAG_MASK);
> }
>
> void *malloc(size_t size)
> {
> return tag_ptr(__libc_malloc(size));
> }
>
> void free(void *ptr)
> {
> __libc_free(untag_ptr(ptr));
> }
>
> void *realloc(void *ptr, size_t size)
> {
> return tag_ptr(__libc_realloc(untag_ptr(ptr), size));
> }
>
> void *calloc(size_t nmemb, size_t size)
> {
> return tag_ptr(__libc_calloc(nmemb, size));
> }