Re: [PATCH] x86/setup: correct off-by-1 in module mapping

[Jan Beulich <jbeulich@suse.com>]

On 19.03.2025 13:15, Roger Pau Monné wrote:
> On Wed, Mar 19, 2025 at 12:21:53PM +0100, Jan Beulich wrote:
>> If a module's length is an exact multiple of PAGE_SIZE, the 2nd argument
>> passed to set_pdx_range() would be one larger than intended. Use
>> PFN_{UP,DOWN}() there instead.
>>
>> Fixes: cd7cc5320bb2 ("x86/boot: add start and size fields to struct boot_module")
>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>>
>> --- a/xen/arch/x86/setup.c
>> +++ b/xen/arch/x86/setup.c
>> @@ -1730,7 +1730,7 @@ void asmlinkage __init noreturn __start_
>>      {
>>          unsigned long s = bi->mods[i].start, l = bi->mods[i].size;
>>  
>> -        set_pdx_range(paddr_to_pfn(s), paddr_to_pfn(s + l) + 1);
>> +        set_pdx_range(PFN_DOWN(s), PFN_UP(s + l));
> 
> Is the set_pdx_range() provided smfn, emfn range inclusive?

No, it's exclusive at the end. See all other uses in this file.

>>          map_pages_to_xen((unsigned long)maddr_to_virt(s), maddr_to_mfn(s),
>>                           PFN_UP(l), PAGE_HYPERVISOR);
> 
> Isn't this line also bogus, as there's no guarantee that the start
> address is aligned to PAGE_SIZE?  And hence the length should take
> into account a possible page offset of s?

See Andrew's reply.

Jan