[PATCH v3] x86: Ensure input to pfn_to_kaddr() is treated as a 64-bit type

[Michael Roth]

On 64-bit platforms, the pfn_to_kaddr() macro requires that the input
value is 64-bits in order to ensure that valid address bits don't get
lost when shifting that input by PAGE_SHIFT to calculate the physical
address to provide a virtual address for.

One such example is in pvalidate_pages() (used by SEV-SNP guests), where
the GFN in the struct used for page-state change requests is a 40-bit
bit-field, so attempts to pass this GFN field directly into
pfn_to_kaddr() ends up causing guest crashes when dealing with addresses
above the 1TB range due to the above.

Fix this issue with SEV-SNP guests, as well as any similar cases that
might cause issues in current/future code, by using a inline function,
instead of the macro, so that the input is implicitly cast to the
expected 64-bit input type prior to performing the shift operation.

While it might be argued that the issue is on the caller side, other
archs/macros have taken similar approaches to deal with instances like
this, such as commit e48866647b48 ("ARM: 8396/1: use phys_addr_t in
pfn_to_kaddr()").

Suggested-by: Dave Hansen <dave.hansen@xxxxxxxxx>
Suggested-by: H. Peter Anvin <hpa@xxxxxxxxx>
Fixes: 6c3211796326 ("x86/sev: Add SNP-specific unaccepted memory support")
Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
---
v3:
  - Use an inline function instead of a macro to handle the cast (Peter)
v2:
  - Move the cast down into pfn_to_kaddr() to fix other possible
    instances (Dave)
  - Rename from "x86/sev: Fix overflow when computing address for
    PVALIDATE"

 arch/x86/include/asm/page.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/page.h b/arch/x86/include/asm/page.h
index d18e5c332cb9..aa8930da42fd 100644
--- a/arch/x86/include/asm/page.h
+++ b/arch/x86/include/asm/page.h
@@ -66,10 +66,14 @@ static inline void copy_user_page(void *to, void *from, unsigned long vaddr,
  * virt_addr_valid(kaddr) returns true.
  */
 #define virt_to_page(kaddr)	pfn_to_page(__pa(kaddr) >> PAGE_SHIFT)
-#define pfn_to_kaddr(pfn)      __va((pfn) << PAGE_SHIFT)
 extern bool __virt_addr_valid(unsigned long kaddr);
 #define virt_addr_valid(kaddr)	__virt_addr_valid((unsigned long) (kaddr))
 
+static inline void *pfn_to_kaddr(unsigned long pfn)
+{
+	return __va(pfn << PAGE_SHIFT);
+}
+
 static __always_inline u64 __canonical_address(u64 vaddr, u8 vaddr_bits)
 {
 	return ((s64)vaddr << (64 - vaddr_bits)) >> (64 - vaddr_bits);
-- 
2.25.1