Messages in this thread | | | Subject | Re: [PATCH 1/1] x86/mm: Fix limit mmap() of /dev/mem to valid physical addresses | From | Ralph Campbell <> | Date | Mon, 25 Mar 2019 15:03:14 -0700 |
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On 3/23/19 12:02 PM, Thomas Gleixner wrote: > Ralph, > > On Mon, 18 Mar 2019, rcampbell@nvidia.com wrote: >> From: Ralph Campbell <rcampbell@nvidia.com> >> >> If CONFIG_DEBUG_VIRTUAL is enabled, a read or write to /dev/mem can >> trigger a VIRTUAL_BUG_ON() depending on the value of high_memory. >> For example: >> >> read_mem() >> valid_phys_addr_range(p=401f1550, count=8) >> __pa(high_memory) >> __phys_addr(x=ffffc88000000000) >> // __START_KERNEL_map = ffffffff80000000 >> // y = ffffc88000000000 - ffffffff80000000 >> VIRTUAL_BUG_ON(phys_addr_valid(400000000000)) >> // boot_cpu_data.x86_phys_bits=46 > > I have no idea why all the irrelevant information in this example would be > helpful, but after extracting the meat I think I know what you want to say. > >> Since by design high_memory is outside the range of valid physical >> addresses, use the non-error checking version __pa_nodebug(high_memory). > > high_memory is not outside the range of valid physical addresses by > design. It's only outside when memory is populated right at the end of the > physical address space. > > So what you really want to say in the changelog is: > > valid_phys_addr_range() is used to sanity check the physical address range > of an operation, e.g. access to /dev/mem. It uses __pa(high_memory) > internally. > > If memory is populated at the end of the physical address space, then > __pa(high_memory) is outside of the physical address space because: > > high_memory = (void *)__va(max_pfn * PAGE_SIZE - 1) + 1; > > For the comparison in valid_phys_addr_range() this is not an issue, but if > CONFIG_DEBUG_VIRTUAL is enabled, __pa() maps to __phys_addr(), which > verifies that the resulting physical address is within the valid physical > address space of the CPU. So in the case that memory is populated at the > end of the physical address space, this is not true and triggers a > VIRTUAL_BUG_ON(). > > Use ... instead, because ... > >> Fixes: be62a32044061cb4a3b70a10598e093f1319102e ("x86/mm: Limit mmap() of > > Please limit the sha1 to the first 12 characters. > >> /dev/mem to valid physical addresses") >> > > No newline between Fixes and the rest please. > >> Signed-off-by: Ralph Campbell <rcampbell@nvidia.com> >
Thanks for the comments. I'll apply them and send a v2 when ready.
>> --- a/arch/x86/mm/mmap.c >> +++ b/arch/x86/mm/mmap.c >> @@ -230,7 +230,7 @@ bool mmap_address_hint_valid(unsigned long addr, unsigned long len) >> /* Can we access it for direct reading/writing? Must be RAM: */ >> int valid_phys_addr_range(phys_addr_t addr, size_t count) >> { >> - return addr + count <= __pa(high_memory); >> + return addr + count <= __pa_nodebug(high_memory); > > This lacks a comment. Aside of that I think there is no point in using > __pa(high_memory) here. This is all about the physical address range. So > this can be simply expressed via: > > return addr + count <= max_pfn * PAGE_SIZE; > > which is much more obvious. > > Thanks, > > tglx
This looks OK to me for x86_64 but looking at arch/x86/mm/init_32.c, initmem_init() sets high_memory based on highstart_pfn or max_low_pfn depending on CONFIG_HIGHMEM. Would using max_pfn in this case work?
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