6.7-stable review patch. If anyone has any objections, please let me know.
------------------
From: Sean Christopherson <seanjc@xxxxxxxxxx>
commit 5ef1d8c1ddbf696e47b226e11888eaf8d9e8e807 upstream.
Do the cache flush of converted pages in svm_register_enc_region() before
dropping kvm->lock to fix use-after-free issues where region and/or its
array of pages could be freed by a different task, e.g. if userspace has
__unregister_enc_region_locked() already queued up for the region.
Note, the "obvious" alternative of using local variables doesn't fully
resolve the bug, as region->pages is also dynamically allocated. I.e. the
region structure itself would be fine, but region->pages could be freed.
Flushing multiple pages under kvm->lock is unfortunate, but the entire
flow is a rare slow path, and the manual flush is only needed on CPUs that
lack coherency for encrypted memory.
Fixes: 19a23da53932 ("Fix unsynchronized access to sev members through svm_register_enc_region")
Reported-by: Gabe Kirkpatrick <gkirkpatrick@xxxxxxxxxx>
Cc: Josh Eads <josheads@xxxxxxxxxx>
Cc: Peter Gonda <pgonda@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Message-Id: <20240217013430.2079561-1-seanjc@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kvm/svm/sev.c | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -1975,20 +1975,22 @@ int sev_mem_enc_register_region(struct k
goto e_free;
}
- region->uaddr = range->addr;
- region->size = range->size;
-
- list_add_tail(®ion->list, &sev->regions_list);
- mutex_unlock(&kvm->lock);
-
/*
* The guest may change the memory encryption attribute from C=0 -> C=1
* or vice versa for this memory range. Lets make sure caches are
* flushed to ensure that guest data gets written into memory with
- * correct C-bit.
+ * correct C-bit. Note, this must be done before dropping kvm->lock,
+ * as region and its array of pages can be freed by a different task
+ * once kvm->lock is released.
*/
sev_clflush_pages(region->pages, region->npages);
+ region->uaddr = range->addr;
+ region->size = range->size;
+
+ list_add_tail(®ion->list, &sev->regions_list);
+ mutex_unlock(&kvm->lock);
+
return ret;
e_free:
