[PATCH v15 17/17] selftests, arm64: add a selftest for passing tagged pointers to kernel
catalin.marinas at arm.com
Wed May 22 14:16:12 UTC 2019
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.
#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;
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)
void free(void *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));
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