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authorEric Biggers <ebiggers@google.com>2020-07-15 23:05:53 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2020-07-23 09:47:13 +0200
commitb34e7e298d7a5ed76b3aa327c240c29f1ef6dd22 (patch)
tree1386eb6469450e813bba9bfe46a81c6129e44354
parentf867c771f98891841c217fa8459244ed0dd28921 (diff)
/dev/mem: Add missing memory barriers for devmem_inode
WRITE_ONCE() isn't the correct way to publish a pointer to a data structure, since it doesn't include a write memory barrier. Therefore other tasks may see that the pointer has been set but not see that the pointed-to memory has finished being initialized yet. Instead a primitive with "release" semantics is needed. Use smp_store_release() for this. The use of READ_ONCE() on the read side is still potentially correct if there's no control dependency, i.e. if all memory being "published" is transitively reachable via the pointer itself. But this pairing is somewhat confusing and error-prone. So just upgrade the read side to smp_load_acquire() so that it clearly pairs with smp_store_release(). Cc: Arnd Bergmann <arnd@arndb.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Kees Cook <keescook@chromium.org> Cc: Matthew Wilcox <willy@infradead.org> Cc: Russell King <linux@arm.linux.org.uk> Cc: Andrew Morton <akpm@linux-foundation.org> Fixes: 3234ac664a87 ("/dev/mem: Revoke mappings when a driver claims the region") Signed-off-by: Eric Biggers <ebiggers@google.com> Cc: stable <stable@vger.kernel.org> Acked-by: Dan Williams <dan.j.williams@intel.com> Link: https://lore.kernel.org/r/20200716060553.24618-1-ebiggers@kernel.org Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--drivers/char/mem.c10
1 files changed, 7 insertions, 3 deletions
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 934c92dcb9ab..687d4af6945d 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -814,7 +814,8 @@ static struct inode *devmem_inode;
#ifdef CONFIG_IO_STRICT_DEVMEM
void revoke_devmem(struct resource *res)
{
- struct inode *inode = READ_ONCE(devmem_inode);
+ /* pairs with smp_store_release() in devmem_init_inode() */
+ struct inode *inode = smp_load_acquire(&devmem_inode);
/*
* Check that the initialization has completed. Losing the race
@@ -1028,8 +1029,11 @@ static int devmem_init_inode(void)
return rc;
}
- /* publish /dev/mem initialized */
- WRITE_ONCE(devmem_inode, inode);
+ /*
+ * Publish /dev/mem initialized.
+ * Pairs with smp_load_acquire() in revoke_devmem().
+ */
+ smp_store_release(&devmem_inode, inode);
return 0;
}