Messages in this thread | | | Date | Sat, 13 Dec 2003 18:08:28 +0000 | Subject | Re: Possible shared mapping bug in 2.4.23 (at least MIPS/Sparc) | From | Peter Horton <> |
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On Sat, Dec 13, 2003 at 05:05:36PM +0100, Ralf Baechle wrote: > On Sat, Dec 13, 2003 at 11:41:34AM +0000, Peter Horton wrote: > > > The current MIPS 2.4 kernel (from CVS) currently allows fixed shared > > mappings to violate D-cache aliasing constraints. > > > > The check for illegal fixed mappings is done in > > arch_get_unmapped_area(), but these mappings are granted in > > get_unmapped_area() and arch_get_unmapped_area() is never called. > > > > A quick look at sparc and sparc64 seem to show the same problem. > > Ehh... <asm/pgtable.h> defines HAVE_ARCH_UNMAPPED_AREA therefore > get_unmapped_area calls the arch's version of arch_get_unmapped_area > instead of the generic version in mm/mmap.c >
arch_get_unmapped_area() never get called because get_unmapped_area() notices the MAP_FIXED flag and returns success.
In the example below the second mmap() should fail because it violates the shm_align_mask.
P.
pdh@qube2:~$ uname -a Linux qube2 2.4.23 #2 Sat Dec 13 18:03:10 GMT 2003 mips unknown pdh@qube2:~$ ./shared 0xdeadbeef 0 pdh@qube2:~$ cat shared.c #include <stdio.h> #include <unistd.h> #include <fcntl.h> #include <sys/mman.h> #include <sys/user.h>
int main(int argc, char *argv[]) { static char zero; void *p1, *p2; int fd;
fd = open("/tmp/test.shared", O_CREAT|O_RDWR|O_TRUNC, 0664); if(fd == -1) return 1; unlink("/tmp/test.shared");
lseek(fd, PAGE_SIZE - 1, SEEK_SET); if(write(fd, &zero, 1) != 1) return 1;
p1 = mmap(NULL, PAGE_SIZE, PROT_READ, MAP_SHARED, fd, 0); if(p1 == MAP_FAILED) return 1;
p2 = mmap(p1 + PAGE_SIZE, PAGE_SIZE, PROT_WRITE, MAP_SHARED|MAP_FIXED, fd, 0); if(p2 == MAP_FAILED || p2 - p1 != PAGE_SIZE) return 1;
*(int *) p2 = 0xdeadbeef;
printf("%#x %#x\n", *(int *) p2, *(int *) p1);
return 0; } pdh@qube2:~$ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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