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.
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)); }