[PATCH] fix empty_zero_page misusage

[Heiko Carstens]

The definition of empty_zero_page is architecture specific.
It is (currently) either a character array, an unsigned long containing
the address of the empty_zero_page, or even worse only the address
of the struct page belonging to the empty_zero_page.

So using empty_zero_page as source address to e.g. clear something may
give random results.
ZERO_PAGE() however returns across all architectures the pointer to
the struct page belonging to the empty_zero_page.

Signed-off-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
---
 drivers/spi/spi-fsl-cpm.c | 3 ++-
 fs/btrfs/ioctl.c          | 4 +++-
 virt/kvm/kvm_main.c       | 5 +++--
 3 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/spi/spi-fsl-cpm.c b/drivers/spi/spi-fsl-cpm.c
index 54b06376f03c..3807bbf8a48f 100644
--- a/drivers/spi/spi-fsl-cpm.c
+++ b/drivers/spi/spi-fsl-cpm.c
@@ -280,6 +280,7 @@ static unsigned long fsl_spi_cpm_get_pram(struct mpc8xxx_spi *mspi)
 
 int fsl_spi_cpm_init(struct mpc8xxx_spi *mspi)
 {
+	const void *zero_page = (const void *) page_to_phys(ZERO_PAGE(0));
 	struct device *dev = mspi->dev;
 	struct device_node *np = dev->of_node;
 	const u32 *iprop;
@@ -324,7 +325,7 @@ int fsl_spi_cpm_init(struct mpc8xxx_spi *mspi)
 		goto err_bds;
 	}
 
-	mspi->dma_dummy_tx = dma_map_single(dev, empty_zero_page, PAGE_SIZE,
+	mspi->dma_dummy_tx = dma_map_single(dev, zero_page, PAGE_SIZE,
 					    DMA_TO_DEVICE);
 	if (dma_mapping_error(dev, mspi->dma_dummy_tx)) {
 		dev_err(dev, "unable to map dummy tx buffer\n");
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 1d04b5559e61..83f2b3e4fbf0 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -368,8 +368,10 @@ static noinline int btrfs_ioctl_fitrim(struct file *file, void __user *arg)
 
 int btrfs_is_empty_uuid(u8 *uuid)
 {
+	const void *zero_page = (const void *) page_to_phys(ZERO_PAGE(0));
+
 	BUILD_BUG_ON(BTRFS_UUID_SIZE > PAGE_SIZE);
-	return !memcmp(uuid, empty_zero_page, BTRFS_UUID_SIZE);
+	return !memcmp(uuid, zero_page, BTRFS_UUID_SIZE);
 }
 
 static noinline int create_subvol(struct inode *dir,
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 662f34c3287e..01edf1c19332 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1615,8 +1615,9 @@ EXPORT_SYMBOL_GPL(kvm_read_guest_cached);
 
 int kvm_clear_guest_page(struct kvm *kvm, gfn_t gfn, int offset, int len)
 {
-	return kvm_write_guest_page(kvm, gfn, (const void *) empty_zero_page,
-				    offset, len);
+	const void *zero_page = (const void *) page_to_phys(ZERO_PAGE(0));
+
+	return kvm_write_guest_page(kvm, gfn, zero_page, offset, len);
 }
 EXPORT_SYMBOL_GPL(kvm_clear_guest_page);
 
-- 
1.8.3.4

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