| Message ID | 20240311161558.1310-1-mhklinux@outlook.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | Handle set_memory_XXcrypted() errors in Hyper-V | expand |
On Mon, Mar 11, 2024 at 09:15:53AM -0700, mhkelley58@gmail.com wrote: > From: Michael Kelley <mhklinux@outlook.com> > Michael Kelley (1): > Drivers: hv: vmbus: Don't free ring buffers that couldn't be > re-encrypted > > Rick Edgecombe (4): > Drivers: hv: vmbus: Leak pages if set_memory_encrypted() fails > Drivers: hv: vmbus: Track decrypted status in vmbus_gpadl > hv_netvsc: Don't free decrypted memory > uio_hv_generic: Don't free decrypted memory > > drivers/hv/channel.c | 16 ++++++++++++---- > drivers/hv/connection.c | 11 +++++++---- > drivers/net/hyperv/netvsc.c | 7 +++++-- > drivers/uio/uio_hv_generic.c | 12 ++++++++---- > include/linux/hyperv.h | 1 + > 5 files changed, 33 insertions(+), 14 deletions(-) Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
On Mon, Mar 11, 2024 at 09:15:53AM -0700, mhkelley58@gmail.com wrote: > From: Michael Kelley <mhklinux@outlook.com> > > Shared (decrypted) pages should never be returned to the page allocator, > lest future usage of the pages store data that should not be exposed to > the host. They may also cause the guest to crash if the page is used in > a way disallowed by HW (i.e. for executable code or as a page table). > > Normally set_memory() call failures are rare. But in CoCo VMs > set_memory_XXcrypted() may involve calls to the untrusted host, and an > attacker could fail these calls such that: > 1. set_memory_encrypted() returns an error and leaves the pages fully > shared. > 2. set_memory_decrypted() returns an error, but the pages are actually > full converted to shared. > > This means that patterns like the below can cause problems: > void *addr = alloc(); > int fail = set_memory_decrypted(addr, 1); > if (fail) > free_pages(addr, 0); > > And: > void *addr = alloc(); > int fail = set_memory_decrypted(addr, 1); > if (fail) { > set_memory_encrypted(addr, 1); > free_pages(addr, 0); > } > > Unfortunately these patterns appear in the kernel. And what the > set_memory() callers should do in this situation is not clear either. They > shouldn’t use them as shared because something clearly went wrong, but > they also need to fully reset the pages to private to free them. But, the > kernel needs the host's help to do this and the host is already being > uncooperative around the needed operations. So this isn't guaranteed to > succeed and the caller is kind of stuck with unusable pages. > > The only choice is to panic or leak the pages. The kernel tries not to > panic if at all possible, so just leak the pages at the call sites. > Separately there is a patch[1] to warn if the guest detects strange host > behavior around this. It is stalled, so in the mean time I’m proceeding > with fixing the callers to leak the pages. No additional warnings are > added, because the plan is to warn in a single place in x86 set_memory() > code. > > This series fixes the cases in the Hyper-V code. > > This is the non-RFC/RFT version of Rick Edgecombe's previous series.[2] > Rick asked me to do this version based on my comments and the testing > I did. I've tested most of the error paths by hacking > set_memory_encrypted() to fail, and observing /proc/vmallocinfo and > /proc/buddyinfo to confirm that the memory is leaked as expected > instead of freed. > > Changes in this version: > * Expanded commit message references to "TDX" to be "CoCo VMs" since > set_memory_encrypted() could fail in other configurations, such as > Hyper-V CoCo guests running with a paravisor on SEV-SNP processors. > * Changed "Subject:" prefixes to match historical practice in Hyper-V > related source files > * Patch 1: Added handling of set_memory_decrypted() failure > * Patch 2: Changed where the "decrypted" flag is set so that > error cases not related to set_memory_encrypted() are handled > correctly > * Patch 2: Fixed the polarity of the test for set_memory_encrypted() > failing > * Added Patch 5 to the series to properly handle free'ing of > ring buffer memory > * Fixed a few typos throughout > > [1] https://lore.kernel.org/lkml/20240122184003.129104-1-rick.p.edgecombe@intel.com/ > [2] https://lore.kernel.org/linux-hyperv/20240222021006.2279329-1-rick.p.edgecombe@intel.com/ > > Michael Kelley (1): > Drivers: hv: vmbus: Don't free ring buffers that couldn't be > re-encrypted > > Rick Edgecombe (4): > Drivers: hv: vmbus: Leak pages if set_memory_encrypted() fails > Drivers: hv: vmbus: Track decrypted status in vmbus_gpadl > hv_netvsc: Don't free decrypted memory > uio_hv_generic: Don't free decrypted memory Applied to hyperv-fixes. Thanks.
On Wed, 2024-04-10 at 21:34 +0000, Wei Liu wrote: > > Applied to hyperv-fixes. Thanks. Thanks, and thanks to Michael for getting it across the finish line.
From: Michael Kelley <mhklinux@outlook.com> Shared (decrypted) pages should never be returned to the page allocator, lest future usage of the pages store data that should not be exposed to the host. They may also cause the guest to crash if the page is used in a way disallowed by HW (i.e. for executable code or as a page table). Normally set_memory() call failures are rare. But in CoCo VMs set_memory_XXcrypted() may involve calls to the untrusted host, and an attacker could fail these calls such that: 1. set_memory_encrypted() returns an error and leaves the pages fully shared. 2. set_memory_decrypted() returns an error, but the pages are actually full converted to shared. This means that patterns like the below can cause problems: void *addr = alloc(); int fail = set_memory_decrypted(addr, 1); if (fail) free_pages(addr, 0); And: void *addr = alloc(); int fail = set_memory_decrypted(addr, 1); if (fail) { set_memory_encrypted(addr, 1); free_pages(addr, 0); } Unfortunately these patterns appear in the kernel. And what the set_memory() callers should do in this situation is not clear either. They shouldn’t use them as shared because something clearly went wrong, but they also need to fully reset the pages to private to free them. But, the kernel needs the host's help to do this and the host is already being uncooperative around the needed operations. So this isn't guaranteed to succeed and the caller is kind of stuck with unusable pages. The only choice is to panic or leak the pages. The kernel tries not to panic if at all possible, so just leak the pages at the call sites. Separately there is a patch[1] to warn if the guest detects strange host behavior around this. It is stalled, so in the mean time I’m proceeding with fixing the callers to leak the pages. No additional warnings are added, because the plan is to warn in a single place in x86 set_memory() code. This series fixes the cases in the Hyper-V code. This is the non-RFC/RFT version of Rick Edgecombe's previous series.[2] Rick asked me to do this version based on my comments and the testing I did. I've tested most of the error paths by hacking set_memory_encrypted() to fail, and observing /proc/vmallocinfo and /proc/buddyinfo to confirm that the memory is leaked as expected instead of freed. Changes in this version: * Expanded commit message references to "TDX" to be "CoCo VMs" since set_memory_encrypted() could fail in other configurations, such as Hyper-V CoCo guests running with a paravisor on SEV-SNP processors. * Changed "Subject:" prefixes to match historical practice in Hyper-V related source files * Patch 1: Added handling of set_memory_decrypted() failure * Patch 2: Changed where the "decrypted" flag is set so that error cases not related to set_memory_encrypted() are handled correctly * Patch 2: Fixed the polarity of the test for set_memory_encrypted() failing * Added Patch 5 to the series to properly handle free'ing of ring buffer memory * Fixed a few typos throughout [1] https://lore.kernel.org/lkml/20240122184003.129104-1-rick.p.edgecombe@intel.com/ [2] https://lore.kernel.org/linux-hyperv/20240222021006.2279329-1-rick.p.edgecombe@intel.com/ Michael Kelley (1): Drivers: hv: vmbus: Don't free ring buffers that couldn't be re-encrypted Rick Edgecombe (4): Drivers: hv: vmbus: Leak pages if set_memory_encrypted() fails Drivers: hv: vmbus: Track decrypted status in vmbus_gpadl hv_netvsc: Don't free decrypted memory uio_hv_generic: Don't free decrypted memory drivers/hv/channel.c | 16 ++++++++++++---- drivers/hv/connection.c | 11 +++++++---- drivers/net/hyperv/netvsc.c | 7 +++++-- drivers/uio/uio_hv_generic.c | 12 ++++++++---- include/linux/hyperv.h | 1 + 5 files changed, 33 insertions(+), 14 deletions(-)