Re: [PATCH v2 2/3] libelf: Expand ELF note printing

From: Jason Andryuk <jason.andryuk@amd.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
	George Dunlap <george.dunlap@citrix.com>,
	Julien Grall <julien@xen.org>,
	Stefano Stabellini <sstabellini@kernel.org>, Wei Liu <wl@xen.org>,
	<xen-devel@lists.xenproject.org>
Subject: Re: [PATCH v2 2/3] libelf: Expand ELF note printing
Date: Thu, 14 Mar 2024 16:36:27 -0400	[thread overview]
Message-ID: <7777da94-4c47-4034-9306-bd8161d6af25@amd.com> (raw)
In-Reply-To: <ab06fce5-eeba-4ab7-97ca-99d876406693@suse.com>

On 2024-03-14 09:16, Jan Beulich wrote:
> On 13.03.2024 20:30, Jason Andryuk wrote:
>> @@ -217,6 +225,15 @@ elf_errorstatus elf_xen_parse_note(struct elf_binary *elf,
>>       case XEN_ELFNOTE_PHYS32_ENTRY:
>>           parms->phys_entry = val;
>>           break;
>> +
>> +    case XEN_ELFNOTE_L1_MFN_VALID:
>> +        if ( elf_uval(elf, note, descsz) != 2 * sizeof(uint64_t) )
>> +            return -1;
> 
> elf_note_numeric() use sites don't have such a check. Why would we need
> one here, and even more so causing a error to be raised when in reality
> the supplied values (still) aren't consumed? Furthermore the documentation
> says "pairs" (plural) for a reason. Finally maddr_t-sized only happens to
> mean uint64_t on all architectures we presently support.

I failed to pay attention to the definition stating plural pairs.  I saw 
Linux stored two 64bit values and printed them.

I added the size check to avoid going out of bounds.  elf_note_numeric() 
handles 1, 2, 4 or 8 bytes and returns 0 otherwise, so it won't overrun 
boundaries.  That's why it was getting printed as "ELF: note: 
L1_MFN_VALID = 0"

What motivated this was seeing "PVH_RELOCATION = 0".  That confusingly 
looks like relocation is disabled.

I'm fine dropping this attempt at printing the L1_MFN_VALID note. 
maddr_t is not defined, and it looks the note values were 32bit in 
non-PAE kernels.  It could just be printed as "ELF: note: L1_MFN_VALID" 
with no details.

Regards,
Jason

>> +        elf_msg(elf, "mask: %#"PRIx64" val: %#"PRIx64"\n",
>> +                elf_note_numeric_array(elf, note, 8, 0),
>> +                elf_note_numeric_array(elf, note, 8, 1));
>> +        break;
>>       }
>>       return 0;
>>   }
> 