[PATCH 6.18 170/198] KVM: SEV: Drop WARN on large size for KVM_MEMORY_ENCRYPT_REG_REGION

Greg Kroah-Hartman
2026-04-20T16:04:32Z

From: Sean Christopherson <seanjc@google.com>

commit 8acffeef5ef720c35e513e322ab08e32683f32f2 upstream.

Drop the WARN in sev_pin_memory() on npages overflowing an int, as the
WARN is comically trivially to trigger from userspace, e.g. by doing:

struct kvm_enc_region range = {
.addr = 0,
.size = -1ul,
};

__vm_ioctl(vm, KVM_MEMORY_ENCRYPT_REG_REGION, &range);

Note, the checks in sev_mem_enc_register_region() that presumably exist to
verify the incoming address+size are completely worthless, as both "addr"
and "size" are u64s and SEV is 64-bit only, i.e. they _can't_ be greater
than ULONG_MAX. That wart will be cleaned up in the near future.

if (range->addr > ULONG_MAX || range->size > ULONG_MAX)
return -EINVAL;

Opportunistically add a comment to explain why the code calculates the
number of pages the "hard" way, e.g. instead of just shifting @ulen.

Fixes: 78824fabc72e ("KVM: SVM: fix svn_pin_memory()'s use of get_user_pages_fast()")
Cc: stable@vger.kernel.org
Reviewed-by: Liam Merwick <liam.merwick@oracle.com>
Tested-by: Liam Merwick <liam.merwick@oracle.com>
Link: https://patch.msgid.link/20260313003302.3136111-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/kvm/svm/sev.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)

--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -679,10 +679,16 @@ static struct page **sev_pin_memory(stru
if (ulen == 0 || uaddr + ulen < uaddr)
return ERR_PTR(-EINVAL);

- /* Calculate number of pages. */
+ /*
+ * Calculate the number of pages that need to be pinned to cover the
+ * entire range. Note! This isn't simply ulen >> PAGE_SHIFT, as KVM
+ * doesn't require the incoming address+size to be page aligned!
+ */
first = (uaddr & PAGE_MASK) >> PAGE_SHIFT;
last = ((uaddr + ulen - 1) & PAGE_MASK) >> PAGE_SHIFT;
npages = (last - first + 1);
+ if (npages > INT_MAX)
+ return ERR_PTR(-EINVAL);

locked = sev->pages_locked + npages;
lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
@@ -691,9 +697,6 @@ static struct page **sev_pin_memory(stru
return ERR_PTR(-ENOMEM);
}

- if (WARN_ON_ONCE(npages > INT_MAX))
- return ERR_PTR(-EINVAL);
-
/* Avoid using vmalloc for smaller buffers. */
size = npages * sizeof(struct page *);
if (size > PAGE_SIZE)