linux-kernel - Re: [herbertx/cryptodev] crypto: arm64/poly1305

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Message-ID: <7a288592-4793-4743-b8ef-c76de1dcca5b@cryptogams.org>
Date: Mon, 5 Aug 2024 17:45:33 +0200
From: Andy Polyakov <appro@...ptogams.org>
To: Justin He <Justin.He@....com>, Herbert Xu <herbert@...dor.apana.org.au>,
 herbertx/cryptodev
 <reply+AAIFISMST74UQEQBJUWW7J6EXDLZNEVBMPHARJBRSY@...ly.github.com>
Cc: herbertx/cryptodev <cryptodev@...eply.github.com>,
 Author <author@...eply.github.com>, "David S. Miller" <davem@...emloft.net>,
 Catalin Marinas <Catalin.Marinas@....com>,
 "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
 Will Deacon <will@...nel.org>,
 "linux-arm-kernel@...ts.infradead.org"
 <linux-arm-kernel@...ts.infradead.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 Ard Biesheuvel <ardb@...nel.org>
Subject: Re: [herbertx/cryptodev] crypto: arm64/poly1305 - move data to rodata
 section (47d9625)

Hi,

>> -----Original Message-----
>> From: Herbert Xu <herbert@...dor.apana.org.au>
>> Sent: Saturday, August 3, 2024 8:40 AM
>> To: herbertx/cryptodev
>> <reply+AAIFISMST74UQEQBJUWW7J6EXDLZNEVBMPHARJBRSY@...ly.github.c
>> om>
>> Cc: herbertx/cryptodev <cryptodev@...eply.github.com>; Author
>> <author@...eply.github.com>; Justin He <Justin.He@....com>; David S. Miller
>> <davem@...emloft.net>; Catalin Marinas <Catalin.Marinas@....com>;
>> linux-crypto@...r.kernel.org; Will Deacon <will@...nel.org>;
>> linux-arm-kernel@...ts.infradead.org; linux-kernel@...r.kernel.org; Ard
>> Biesheuvel <ardb@...nel.org>; Andy Polyakov <appro@...ptogams.org>
>> Subject: Re: [herbertx/cryptodev] crypto: arm64/poly1305 - move data to
>> rodata section (47d9625)
>>
>> On Fri, Aug 02, 2024 at 08:09:10AM -0700, Andy Polyakov wrote:
>>> Formally speaking this is error prone, because there is no guarantee that linker
>> will be able to resolve it as argument to `adr` instruction above. I mean since the
>> address is resolved with `adr` instruction alone, there is a limit on how far the
>> label can be from the instruction in question. On a practical level, if/since it's
>> compiled as part of a kernel module, it won't be a problem, because the module
>> won't be large enough to break the limit, but it **is** a problem in general case.
> Thanks,
> Can this problem be resolved by changing "adr" to "adrp"?

Not by adrp alone, it has to be complemented with addition. I mean addrp 
gives you the label's page address and you need to add the offset within 
the page.

>>> But why would objtool attempt to disassemble it? Does it actually attempt to
>> disassemble unreferenced spaces between functions? Note that the .Lzeros label
>> doesn't make it into .o file, so there won't be anything in the symbol table to
>> discover as potential entry point..
> There is a similar patch (1253cab8a352) for x86. I guess that objtool/stacktool can be improved in this regard.

objtool is weird and arguably inconsistent. It does look at the symbol 
table(*), and detects the return instructions(**), yet insists on 
disassemble-ability of the whole .text segment... Oh well...

Cheers.

(*) For example it refuses to generated ORC metadata for the following 
snippet

.text
foo: ret

It insists on foo being complemented with '.type foo,@function' as well 
as meaningful .size.

(**) Since it does mark the region[s] past 'ret' as type:(und)