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vfio-pci: Avoid recursive read-lock usage

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A down_read on memory_lock is held when performing read/write accesses
to MMIO BAR space, including across the copy_to/from_user() callouts
which may fault.  If the user buffer for these copies resides in an
mmap of device MMIO space, the mmap fault handler will acquire a
recursive read-lock on memory_lock.  Avoid this by reducing the lock
granularity.  Sequential accesses requiring multiple ioread/iowrite
cycles are expected to be rare, therefore typical accesses should not
see additional overhead.

VGA MMIO accesses are expected to be non-fatal regardless of the PCI
memory enable bit to allow legacy probing, this behavior remains with
a comment added.  ioeventfds are now included in memory access testing,
with writes dropped while memory space is disabled.

Fixes: abafbc551f ("vfio-pci: Invalidate mmaps and block MMIO access on disabled memory")
Reported-by: Zhiyi Guo <zhguo@redhat.com>
Tested-by: Zhiyi Guo <zhguo@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
This commit is contained in:
Alex Williamson 2020-08-17 11:08:18 -06:00
parent 9123e3a74e
commit bc93b9ae01
2 changed files with 98 additions and 24 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
drivers/vfio/pci/vfio_pci_private.h
View File

@ -33,12 +33,14 @@
struct vfio_pci_ioeventfd {
struct list_head next;
struct vfio_pci_device *vdev;
struct virqfd *virqfd;
void __iomem *addr;
uint64_t data;
loff_t pos;
int bar;
int count;
bool test_mem;
};
struct vfio_pci_irq_ctx {

120
drivers/vfio/pci/vfio_pci_rdwr.c
View File

@ -37,17 +37,70 @@
#define vfio_ioread8 ioread8
#define vfio_iowrite8 iowrite8
#define VFIO_IOWRITE(size) \
static int vfio_pci_iowrite##size(struct vfio_pci_device *vdev, \
bool test_mem, u##size val, void __iomem *io) \
{ \
if (test_mem) { \
down_read(&vdev->memory_lock); \
if (!__vfio_pci_memory_enabled(vdev)) { \
up_read(&vdev->memory_lock); \
return -EIO; \
} \
} \
\
vfio_iowrite##size(val, io); \
\
if (test_mem) \
up_read(&vdev->memory_lock); \
\
return 0; \
}
VFIO_IOWRITE(8)
VFIO_IOWRITE(16)
VFIO_IOWRITE(32)
#ifdef iowrite64
VFIO_IOWRITE(64)
#endif
#define VFIO_IOREAD(size) \
static int vfio_pci_ioread##size(struct vfio_pci_device *vdev, \
bool test_mem, u##size *val, void __iomem *io) \
{ \
if (test_mem) { \
down_read(&vdev->memory_lock); \
if (!__vfio_pci_memory_enabled(vdev)) { \
up_read(&vdev->memory_lock); \
return -EIO; \
} \
} \
\
*val = vfio_ioread##size(io); \
\
if (test_mem) \
up_read(&vdev->memory_lock); \
\
return 0; \
}
VFIO_IOREAD(8)
VFIO_IOREAD(16)
VFIO_IOREAD(32)
/*
* Read or write from an __iomem region (MMIO or I/O port) with an excluded
* range which is inaccessible. The excluded range drops writes and fills
* reads with -1. This is intended for handling MSI-X vector tables and
* leftover space for ROM BARs.
*/
static ssize_t do_io_rw(void __iomem *io, char __user *buf,
static ssize_t do_io_rw(struct vfio_pci_device *vdev, bool test_mem,
void __iomem *io, char __user *buf,
loff_t off, size_t count, size_t x_start,
size_t x_end, bool iswrite)
{
ssize_t done = 0;
int ret;
while (count) {
size_t fillable, filled;
@ -66,9 +119,15 @@ static ssize_t do_io_rw(void __iomem *io, char __user *buf,
if (copy_from_user(&val, buf, 4))
return -EFAULT;
vfio_iowrite32(val, io + off);
ret = vfio_pci_iowrite32(vdev, test_mem,
val, io + off);
if (ret)
return ret;
} else {
val = vfio_ioread32(io + off);
ret = vfio_pci_ioread32(vdev, test_mem,
&val, io + off);
if (ret)
return ret;
if (copy_to_user(buf, &val, 4))
return -EFAULT;
@ -82,9 +141,15 @@ static ssize_t do_io_rw(void __iomem *io, char __user *buf,
if (copy_from_user(&val, buf, 2))
return -EFAULT;
vfio_iowrite16(val, io + off);
ret = vfio_pci_iowrite16(vdev, test_mem,
val, io + off);
if (ret)
return ret;
} else {
val = vfio_ioread16(io + off);
ret = vfio_pci_ioread16(vdev, test_mem,
&val, io + off);
if (ret)
return ret;
if (copy_to_user(buf, &val, 2))
return -EFAULT;
@ -98,9 +163,15 @@ static ssize_t do_io_rw(void __iomem *io, char __user *buf,
if (copy_from_user(&val, buf, 1))
return -EFAULT;
vfio_iowrite8(val, io + off);
ret = vfio_pci_iowrite8(vdev, test_mem,
val, io + off);
if (ret)
return ret;
} else {
val = vfio_ioread8(io + off);
ret = vfio_pci_ioread8(vdev, test_mem,
&val, io + off);
if (ret)
return ret;
if (copy_to_user(buf, &val, 1))
return -EFAULT;
@ -178,14 +249,6 @@ ssize_t vfio_pci_bar_rw(struct vfio_pci_device *vdev, char __user *buf,
count = min(count, (size_t)(end - pos));
if (res->flags & IORESOURCE_MEM) {
down_read(&vdev->memory_lock);
if (!__vfio_pci_memory_enabled(vdev)) {
up_read(&vdev->memory_lock);
return -EIO;
}
}
if (bar == PCI_ROM_RESOURCE) {
/*
* The ROM can fill less space than the BAR, so we start the
@ -213,7 +276,8 @@ ssize_t vfio_pci_bar_rw(struct vfio_pci_device *vdev, char __user *buf,
x_end = vdev->msix_offset + vdev->msix_size;
}
done = do_io_rw(io, buf, pos, count, x_start, x_end, iswrite);
done = do_io_rw(vdev, res->flags & IORESOURCE_MEM, io, buf, pos,
count, x_start, x_end, iswrite);
if (done >= 0)
*ppos += done;
@ -221,9 +285,6 @@ ssize_t vfio_pci_bar_rw(struct vfio_pci_device *vdev, char __user *buf,
if (bar == PCI_ROM_RESOURCE)
pci_unmap_rom(pdev, io);
out:
if (res->flags & IORESOURCE_MEM)
up_read(&vdev->memory_lock);
return done;
}
@ -278,7 +339,12 @@ ssize_t vfio_pci_vga_rw(struct vfio_pci_device *vdev, char __user *buf,
return ret;
}
done = do_io_rw(iomem, buf, off, count, 0, 0, iswrite);
/*
* VGA MMIO is a legacy, non-BAR resource that hopefully allows
* probing, so we don't currently worry about access in relation
* to the memory enable bit in the command register.
*/
done = do_io_rw(vdev, false, iomem, buf, off, count, 0, 0, iswrite);
vga_put(vdev->pdev, rsrc);
@ -296,17 +362,21 @@ static int vfio_pci_ioeventfd_handler(void *opaque, void *unused)
switch (ioeventfd->count) {
case 1:
vfio_iowrite8(ioeventfd->data, ioeventfd->addr);
vfio_pci_iowrite8(ioeventfd->vdev, ioeventfd->test_mem,
ioeventfd->data, ioeventfd->addr);
break;
case 2:
vfio_iowrite16(ioeventfd->data, ioeventfd->addr);
vfio_pci_iowrite16(ioeventfd->vdev, ioeventfd->test_mem,
ioeventfd->data, ioeventfd->addr);
break;
case 4:
vfio_iowrite32(ioeventfd->data, ioeventfd->addr);
vfio_pci_iowrite32(ioeventfd->vdev, ioeventfd->test_mem,
ioeventfd->data, ioeventfd->addr);
break;
#ifdef iowrite64
case 8:
vfio_iowrite64(ioeventfd->data, ioeventfd->addr);
vfio_pci_iowrite64(ioeventfd->vdev, ioeventfd->test_mem,
ioeventfd->data, ioeventfd->addr);
break;
#endif
}
@ -378,11 +448,13 @@ long vfio_pci_ioeventfd(struct vfio_pci_device *vdev, loff_t offset,
goto out_unlock;
}
ioeventfd->vdev = vdev;
ioeventfd->addr = vdev->barmap[bar] + pos;
ioeventfd->data = data;
ioeventfd->pos = pos;
ioeventfd->bar = bar;
ioeventfd->count = count;
ioeventfd->test_mem = vdev->pdev->resource[bar].flags & IORESOURCE_MEM;
ret = vfio_virqfd_enable(ioeventfd, vfio_pci_ioeventfd_handler,
NULL, NULL, &ioeventfd->virqfd, fd);