memremap: check pfn validity before passing to pfn_to_page()

In memremap's helper function try_ram_remap(), we dereference a struct
page pointer that was derived from a PFN that is known to be covered by
a 'System RAM' iomem region, and is thus assumed to be a 'valid' PFN,
i.e., a PFN that has a struct page associated with it and is covered by
the kernel direct mapping.

However, the assumption that there is a 1:1 relation between the System
RAM iomem region and the kernel direct mapping is not universally valid
on all architectures, and on ARM and arm64, 'System RAM' may include
regions for which pfn_valid() returns false.

Generally speaking, both __va() and pfn_to_page() should only ever be
called on PFNs/physical addresses for which pfn_valid() returns true, so
add that check to try_ram_remap().

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/kernel/memremap.c b/kernel/memremap.c
index 60baf4d3401e6c6ae209a0fb581bbd7f40392743..6cf54615a9c45181b8efdb6b61975b490b525b8f 100644 (file)
--- a/kernel/memremap.c
+++ b/kernel/memremap.c
@@ -29,10 +29,10 @@ __weak void __iomem *ioremap_cache(resource_size_t offset, unsigned long size)
 
 static void *try_ram_remap(resource_size_t offset, size_t size)
 {
-       struct page *page = pfn_to_page(offset >> PAGE_SHIFT);
+       unsigned long pfn = PHYS_PFN(offset);
 
        /* In the simple case just return the existing linear address */
-       if (!PageHighMem(page))
+       if (pfn_valid(pfn) && !PageHighMem(pfn_to_page(pfn)))
                return __va(offset);
        return NULL; /* fallback to ioremap_cache */
 }