[v3,kvmtool,05/32] Check that a PCI device's memory size is power of two

Commit Message

Alexandru Elisei March 26, 2020, 3:24 p.m. UTC

According to the PCI local bus specification [1], a device's memory size
must be a power of two. This is also implicit in the mechanism that a CPU
uses to get the memory size requirement for a PCI device.

The vesa device requests a memory size that isn't a power of two.
According to the same spec [1], a device is allowed to consume more memory
than it actually requires. As a result, the amount of memory that the vesa
device now reserves has been increased.

To prevent slip-ups in the future, a few BUILD_BUG_ON statements were added
in places where the memory size is known at compile time.

[1] PCI Local Bus Specification Revision 3.0, section 6.2.5.1

Reviewed-by: Andre Przywara <[e-mail]>
Signed-off-by: Alexandru Elisei <[e-mail]>
---
 hw/vesa.c          | 3 +++
 include/kvm/util.h | 2 ++
 include/kvm/vesa.h | 6 +++++-
 virtio/pci.c       | 3 +++
 4 files changed, 13 insertions(+), 1 deletion(-)

Patch

diff --git a/hw/vesa.c b/hw/vesa.c
index f3c5114cf4fe..d75b4b316a1e 100644
--- a/hw/vesa.c
+++ b/hw/vesa.c
@@ -58,6 +58,9 @@  struct framebuffer *vesa__init(struct kvm *kvm)
 	char *mem;
 	int r;
 
+	BUILD_BUG_ON(!is_power_of_two(VESA_MEM_SIZE));
+	BUILD_BUG_ON(VESA_MEM_SIZE < VESA_BPP/8 * VESA_WIDTH * VESA_HEIGHT);
+
 	if (!kvm->cfg.vnc && !kvm->cfg.sdl && !kvm->cfg.gtk)
 		return NULL;
 
diff --git a/include/kvm/util.h b/include/kvm/util.h
index 4ca7aa9392b6..199724c4018c 100644
--- a/include/kvm/util.h
+++ b/include/kvm/util.h
@@ -104,6 +104,8 @@  static inline unsigned long roundup_pow_of_two(unsigned long x)
 	return x ? 1UL << fls_long(x - 1) : 0;
 }
 
+#define is_power_of_two(x)	((x) > 0 ? ((x) & ((x) - 1)) == 0 : 0)
+
 struct kvm;
 void *mmap_hugetlbfs(struct kvm *kvm, const char *htlbfs_path, u64 size);
 void *mmap_anon_or_hugetlbfs(struct kvm *kvm, const char *hugetlbfs_path, u64 size);
diff --git a/include/kvm/vesa.h b/include/kvm/vesa.h
index 0fac11ab5a9f..e7d971343642 100644
--- a/include/kvm/vesa.h
+++ b/include/kvm/vesa.h
@@ -5,8 +5,12 @@ 
 #define VESA_HEIGHT	480
 
 #define VESA_MEM_ADDR	0xd0000000
-#define VESA_MEM_SIZE	(4*VESA_WIDTH*VESA_HEIGHT)
 #define VESA_BPP	32
+/*
+ * We actually only need VESA_BPP/8*VESA_WIDTH*VESA_HEIGHT bytes. But the memory
+ * size must be a power of 2, so we round up.
+ */
+#define VESA_MEM_SIZE	(1 << 21)
 
 struct kvm;
 struct biosregs;
diff --git a/virtio/pci.c b/virtio/pci.c
index 99653cad2c0f..04e801827df9 100644
--- a/virtio/pci.c
+++ b/virtio/pci.c
@@ -435,6 +435,9 @@  int virtio_pci__init(struct kvm *kvm, void *dev, struct virtio_device *vdev,
 	vpci->kvm = kvm;
 	vpci->dev = dev;
 
+	BUILD_BUG_ON(!is_power_of_two(IOPORT_SIZE));
+	BUILD_BUG_ON(!is_power_of_two(PCI_IO_SIZE));
+
 	r = ioport__register(kvm, IOPORT_EMPTY, &virtio_pci__io_ops, IOPORT_SIZE, vdev);
 	if (r < 0)
 		return r;