mirror of https://github.com/torvalds/linux.git
64e455079e
For VMAs that don't want write notifications, PTEs created for read faults
have their write bit set. If the read fault happens after VM_SOFTDIRTY is
cleared, then the PTE's softdirty bit will remain clear after subsequent
writes.
Here's a simple code snippet to demonstrate the bug:
char* m = mmap(NULL, getpagesize(), PROT_READ | PROT_WRITE,
MAP_ANONYMOUS | MAP_SHARED, -1, 0);
system("echo 4 > /proc/$PPID/clear_refs"); /* clear VM_SOFTDIRTY */
assert(*m == '\0'); /* new PTE allows write access */
assert(!soft_dirty(x));
*m = 'x'; /* should dirty the page */
assert(soft_dirty(x)); /* fails */
With this patch, write notifications are enabled when VM_SOFTDIRTY is
cleared. Furthermore, to avoid unnecessary faults, write notifications
are disabled when VM_SOFTDIRTY is set.
As a side effect of enabling and disabling write notifications with
care, this patch fixes a bug in mprotect where vm_page_prot bits set by
drivers were zapped on mprotect. An analogous bug was fixed in mmap by
commit
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| .. | ||
| Kconfig | ||
| Makefile | ||
| array.c | ||
| base.c | ||
| cmdline.c | ||
| consoles.c | ||
| cpuinfo.c | ||
| devices.c | ||
| fd.c | ||
| fd.h | ||
| generic.c | ||
| inode.c | ||
| internal.h | ||
| interrupts.c | ||
| kcore.c | ||
| kmsg.c | ||
| loadavg.c | ||
| meminfo.c | ||
| namespaces.c | ||
| nommu.c | ||
| page.c | ||
| proc_net.c | ||
| proc_sysctl.c | ||
| proc_tty.c | ||
| root.c | ||
| self.c | ||
| softirqs.c | ||
| stat.c | ||
| task_mmu.c | ||
| task_nommu.c | ||
| thread_self.c | ||
| uptime.c | ||
| version.c | ||
| vmcore.c | ||