Messages in this thread Patch in this message | | | Date | Thu, 23 Nov 2023 11:15:02 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH v3] x86: Ensure input to pfn_to_kaddr() is treated as a 64-bit type |
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* Michael Roth <michael.roth@amd.com> wrote:
> 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@intel.com> > Suggested-by: H. Peter Anvin <hpa@zytor.com> > Fixes: 6c3211796326 ("x86/sev: Add SNP-specific unaccepted memory support") > Signed-off-by: Michael Roth <michael.roth@amd.com> > --- > 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); > +}
Makes sense I guess.
Note that in the tip:x86/mm commit I changed it to __always_inline, as we typically do for such low level MM helpers. Delta patch below.
Thanks,
Ingo
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arch/x86/include/asm/page.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/page.h b/arch/x86/include/asm/page.h index aa8930da42fd..1b93ff80b43b 100644 --- a/arch/x86/include/asm/page.h +++ b/arch/x86/include/asm/page.h @@ -69,7 +69,7 @@ static inline void copy_user_page(void *to, void *from, unsigned long vaddr, 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) +static __always_inline void *pfn_to_kaddr(unsigned long pfn) { return __va(pfn << PAGE_SHIFT); }
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