Re: [PATCH kernel] KVM: PPC: Book3S: Suppress warnings when allocating too big memory slots

On 02/09/2021 00:59, Fabiano Rosas wrote:

Alexey Kardashevskiy [off-list ref] writes:

quoted

The userspace can trigger "vmalloc size %lu allocation failure: exceeds
total pages" via the KVM_SET_USER_MEMORY_REGION ioctl.

This silences the warning by checking the limit before calling vzalloc()
and returns ENOMEM if failed.

This does not call underlying valloc helpers as __vmalloc_node() is only
exported when CONFIG_TEST_VMALLOC_MODULE and __vmalloc_node_range() is not
exported at all.

Spotted by syzkaller.

Signed-off-by: Alexey Kardashevskiy <redacted>
---
  arch/powerpc/kvm/book3s_hv.c | 8 ++++++--
  1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 474c0cfde384..a59f1cccbcf9 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c

@@ -4830,8 +4830,12 @@ static int kvmppc_core_prepare_memory_region_hv(struct kvm *kvm,
  	unsigned long npages = mem->memory_size >> PAGE_SHIFT;

  	if (change == KVM_MR_CREATE) {
-		slot->arch.rmap = vzalloc(array_size(npages,
-					  sizeof(*slot->arch.rmap)));
+		unsigned long cb = array_size(npages, sizeof(*slot->arch.rmap));

What does cb mean?

"count of bytes"

This is from my deep Windows past :)

https://docs.microsoft.com/en-us/windows/win32/stg/coding-style-conventions

quoted

+
+		if ((cb >> PAGE_SHIFT) > totalram_pages())
+			return -ENOMEM;
+
+		slot->arch.rmap = vzalloc(cb);
  		if (!slot->arch.rmap)
  			return -ENOMEM;
  	}

-- 
Alexey