linux-kernel - Re: [PATCH v2] kallsyms: Fix wrong "big" kernel symbol type read from procfs

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20241012024745.3807a071.gary@garyguo.net>
Date: Sat, 12 Oct 2024 02:47:45 +0100
From: Gary Guo <gary@...yguo.net>
To: Matthew Wilcox <willy@...radead.org>
Cc: Zheng Yejian <zhengyejian@...weicloud.com>, arnd@...db.de,
 kees@...nel.org, mcgrof@...nel.org, masahiroy@...nel.org,
 ndesaulniers@...gle.com, ardb@...nel.org, jannh@...gle.com,
 song@...nel.org, boqun.feng@...il.com, gregkh@...uxfoundation.org,
 linux-kernel@...r.kernel.org, yeweihua4@...wei.com
Subject: Re: [PATCH v2] kallsyms: Fix wrong "big" kernel symbol type read
 from procfs

On Fri, 11 Oct 2024 23:01:12 +0100
Matthew Wilcox <willy@...radead.org> wrote:

> On Fri, Oct 11, 2024 at 10:38:53PM +0800, Zheng Yejian wrote:
> > The root cause is that, after commit 73bbb94466fd ("kallsyms: support
> > "big" kernel symbols"), ULEB128 was used to encode symbol name length.
> > That is, for "big" kernel symbols of which name length is longer than
> > 0x7f characters, the length info is encoded into 2 bytes.  
> 
> Technically, at least two.  If we ever have a symbol larger than
> 16kB, we'll use three bytes.

Let's not worry about things that would not happen.

scripts/kallsyms.c have a check to ensure that symbol names don't get
longer than 0x3FFF.

Best,
Gary

> 
> > +++ b/kernel/kallsyms.c
> > @@ -103,8 +103,11 @@ static char kallsyms_get_symbol_type(unsigned int off)
> >  {
> >  	/*
> >  	 * Get just the first code, look it up in the token table,
> > -	 * and return the first char from this token.
> > +	 * and return the first char from this token. If MSB of length
> > +	 * is 1, it is a "big" symbol, so needs an additional byte.
> >  	 */
> > +	if (kallsyms_names[off] & 0x80)
> > +		off++;  
> 
> So this "if" should be a "while" for maximum future proofing against the
> day that we have a 16kB function ...
>