drivers/virt/acrn: fix PFNMAP PTE checks in acrn_vm_ram_map()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: drivers/virt/acrn: fix PFNMAP PTE checks in acrn_vm_ram_map() Patch series "mm: follow_pte() improvements and acrn follow_pte() fixes". Patch #1 fixes a bunch of issues I spotted in the acrn driver. It compiles, that's all I know. I'll appreciate some review and testing from acrn folks. Patch #2+#3 improve follow_pte(), passing a VMA instead of the MM, adding more sanity checks, and improving the documentation. Gave it a quick test on x86-64 using VM_PAT that ends up using follow_pte(). This patch (of 3): We currently miss handling various cases, resulting in a dangerous follow_pte() (previously follow_pfn()) usage. (1) We're not checking PTE write permissions. Maybe we should simply always require pte_write() like we do for pin_user_pages_fast(FOLL_WRITE)? Hard to tell, so let's check for ACRN_MEM_ACCESS_WRITE for now. (2) We're not rejecting refcounted pages. As we are not using MMU notifiers, messing with refcounted pages is dangerous and can result in use-after-free. Let's make sure to reject them. (3) We are only looking at the first PTE of a bigger range. We only lookup a single PTE, but memmap->len may span a larger area. Let's loop over all involved PTEs and make sure the PFN range is actually contiguous. Reject everything else: it couldn't have worked either way, and rather made use access PFNs we shouldn't be accessing.

References

• https://git.kernel.org/stable/c/5c6705aa47b5b78d7ad36fea832bb69caa5bf49a
• https://git.kernel.org/stable/c/afeb0e69627695f759fc73c39c1640dbf8649b32
• https://git.kernel.org/stable/c/e873f36ec890bece26ecce850e969917bceebbb6
• https://git.kernel.org/stable/c/4c4ba3cf3a15ccfbaf787d0296fa42cdb00da9b4
• https://git.kernel.org/stable/c/2c8d6e24930b8ef7d4a81787627c559ae0e0d3bb
• https://git.kernel.org/stable/c/3d6586008f7b638f91f3332602592caa8b00b559