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pkeys.7: Cosmetic changes to example program 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2016-10-13 11:49:00 +02:00
parent 435f231ac9
commit 8bb4e76704
1 changed files with 62 additions and 39 deletions
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101
man7/pkeys.7
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@ -165,81 +165,104 @@ Segmentation fault (core dumped)
#include <stdio.h>
#include <sys/mman.h>
static inline void wrpkru(unsigned int pkru)
static inline void
wrpkru(unsigned int pkru)
{
unsigned int eax = pkru;
unsigned int ecx = 0;
unsigned int edx = 0;
unsigned int eax = pkru;
unsigned int ecx = 0;
unsigned int edx = 0;
asm volatile(".byte 0x0f,0x01,0xef\n\t"
: : "a" (eax), "c" (ecx), "d" (edx));
asm volatile(".byte 0x0f,0x01,0xef\\n\\t"
: : "a" (eax), "c" (ecx), "d" (edx));
}
int pkey_set(int pkey, unsigned long rights, unsigned long flags)
int
pkey_set(int pkey, unsigned long rights, unsigned long flags)
{
unsigned int pkru = (rights << (2*pkey));
unsigned int pkru = (rights << (2 * pkey));
return wrpkru(pkru);
}
int pkey_mprotect(void *ptr, size_t size, unsigned long orig_prot, unsigned long pkey)
int
pkey_mprotect(void *ptr, size_t size, unsigned long orig_prot,
unsigned long pkey)
{
return syscall(SYS_pkey_mprotect, ptr, size, orig_prot, pkey);
}
int pkey_alloc(void)
int
pkey_alloc(void)
{
return syscall(SYS_pkey_alloc, 0, 0);
}
int pkey_free(unsigned long pkey)
int
pkey_free(unsigned long pkey)
{
return syscall(SYS_pkey_free, pkey);
}
int main(void)
#define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); \\
} while (0)
int
main(void)
{
int status;
int pkey;
int *buffer;
/* Allocate one page of memory: */
buffer = mmap(NULL, getpagesize(), PROT_READ|PROT_WRITE, MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
/*
*Allocate one page of memory
*/
buffer = mmap(NULL, getpagesize(), PROT_READ | PROT_WRITE,
MAP_ANONYMOUS | MAP_PRIVATE, \-1, 0);
if (buffer == MAP_FAILED)
return -ENOMEM;
/* Put some random data in to the page (still OK to touch): */
(*buffer) = __LINE__;
printf("buffer contains: %d\\n", *buffer);
/* Allocate a protection key: */
pkey = pkey_alloc();
if (pkey < 0)
return pkey;
/* Disable access to any memory with "pkey" set,
* even though there is none right now. */
status = pkey_set(pkey, PKEY_DISABLE_ACCESS, 0);
if (status)
return status;
errExit("mmap");
/*
* set the protection key on "buffer":
* Note that it is still read/write as far as mprotect() is,
* Put some random data into the page (still OK to touch)
*/
*buffer = __LINE__;
printf("buffer contains: %d\\n", *buffer);
/*
* Allocate a protection key:
*/
pkey = pkey_alloc();
if (pkey == \-1)
errExit("pkey_alloc");
/*
* Disable access to any memory with "pkey" set,
* even though there is none right now
*/
status = pkey_set(pkey, PKEY_DISABLE_ACCESS, 0);
if (status)
errExit("pkey_set");
/*
* Set the protection key on "buffer".
* Note that it is still read/write as far as mprotect() is
* concerned and the previous pkey_set() overrides it.
*/
status = pkey_mprotect(buffer, getpagesize(), PROT_READ|PROT_WRITE, pkey);
if (status)
return status;
status = pkey_mprotect(buffer, getpagesize(),
PROT_READ | PROT_WRITE, pkey);
if (status == -1)
errExit("pkey_mprotect");
printf("about to read buffer again...\\n");
/* this will crash, because we have disallowed access: */
/*
* This will crash, because we have disallowed access
*/
printf("buffer contains: %d\\n", *buffer);
status = pkey_free(pkey);
if (status)
return status;
if (status == -1)
errExit("pkey_free");
return 0;
exit(EXIT_SUCCESS);
}
.SH SEE ALSO
.BR pkey_alloc (2),