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Re: [PATCH] x86/setup: correct off-by-1 in module mapping
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 19 Mar 2025 13:40:55 +0100
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Daniel Smith <dpsmith@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 19 Mar 2025 12:41:00 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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@xxxxxxxx>
>>
>> --- 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
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