On 5/28/19 7:05 PM, Paul Burton wrote:
> The virt_addr_valid() function is meant to return true iff
> virt_to_page() will return a valid struct page reference. This is true
> iff the address provided is found within the unmapped address range
> between PAGE_OFFSET & MAP_BASE, but we don't currently check for that
> condition. Instead we simply mask the address to obtain what will be a
> physical address if the virtual address is indeed in the desired range,
> shift it to form a PFN & then call pfn_valid(). This can incorrectly
> return true if called with a virtual address which, after masking,
> happens to form a physical address corresponding to a valid PFN.
>
> For example we may vmalloc an address in the kernel mapped region
> starting a MAP_BASE & obtain the virtual address:
>
> addr = 0xc000000000002000
>
> When masked by virt_to_phys(), which uses __pa() & in turn CPHYSADDR(),
> we obtain the following (bogus) physical address:
>
> addr = 0x2000
>
> In a common system with PHYS_OFFSET=0 this will correspond to a valid
> struct page which should really be accessed by virtual address
> PAGE_OFFSET+0x2000, causing virt_addr_valid() to incorrectly return 1
> indicating that the original address corresponds to a struct page.
>
> This is equivalent to the ARM64 change made in commit ca219452c6b8
> ("arm64: Correctly bounds check virt_addr_valid").
>
> This fixes fallout when hardened usercopy is enabled caused by the
> related commit 517e1fbeb65f ("mm/usercopy: Drop extra
> is_vmalloc_or_module() check") which removed a check for the vmalloc
> range that was present from the introduction of the hardened usercopy
> feature.
>
> Signed-off-by: Paul Burton <paul.burton@xxxxxxxx>
> References: ca219452c6b8 ("arm64: Correctly bounds check virt_addr_valid")
> References: 517e1fbeb65f ("mm/usercopy: Drop extra is_vmalloc_or_module() check")
> Reported-by: Julien Cristau <jcristau@xxxxxxxxxx>
> Tested-by: YunQiang Su <ysu@xxxxxxxxxxxx>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@xxxxxxxxx>
> URL: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=929366
> Cc: stable@xxxxxxxxxxxxxxx # v4.12+
> ---
>
> arch/mips/mm/mmap.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/arch/mips/mm/mmap.c b/arch/mips/mm/mmap.c
> index 2f616ebeb7e0..7755a1fad05a 100644
> --- a/arch/mips/mm/mmap.c
> +++ b/arch/mips/mm/mmap.c
> @@ -203,6 +203,11 @@ unsigned long arch_randomize_brk(struct mm_struct *mm)
>
> int __virt_addr_valid(const volatile void *kaddr)
> {
> + unsigned long vaddr = (unsigned long)vaddr;
> +
> + if ((vaddr < PAGE_OFFSET) || (vaddr >= MAP_BASE))
> + return 0;
> +
> return pfn_valid(PFN_DOWN(virt_to_phys(kaddr)));
> }
> EXPORT_SYMBOL_GPL(__virt_addr_valid);
>
