linux-kernel - Re: [PATCH v2 1/2] x86/kgdb: convert early breakpoints to poke breakpoints

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: <874j7pshbb.ffs@tglx>
Date: Mon, 12 Aug 2024 20:54:16 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Florian Rommel <mail@...rommel.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 "H . Peter Anvin" <hpa@...or.com>, Jason Wessel
 <jason.wessel@...driver.com>, Daniel Thompson
 <daniel.thompson@...aro.org>, Douglas Anderson <dianders@...omium.org>,
 Lorena Kretzschmar <qy15sije@....cs.fau.de>, Stefan Saecherl
 <stefan.saecherl@....de>, Peter Zijlstra <peterz@...radead.org>,
 Christophe JAILLET <christophe.jaillet@...adoo.fr>, Randy Dunlap
 <rdunlap@...radead.org>, Masami Hiramatsu <mhiramat@...nel.org>, Andrew
 Morton <akpm@...ux-foundation.org>, Christophe Leroy
 <christophe.leroy@...roup.eu>, Geert Uytterhoeven
 <geert+renesas@...der.be>, kgdb-bugreport@...ts.sourceforge.net,
 x86@...nel.org, linux-kernel@...r.kernel.org
Cc: Florian Rommel <mail@...rommel.de>
Subject: Re: [PATCH v2 1/2] x86/kgdb: convert early breakpoints to poke
 breakpoints

Florian!

On Mon, Aug 12 2024 at 19:43, Florian Rommel wrote:
> On x86, after booting, the kernel text is read-only.  Then, KGDB has to
> use the text_poke mechanism to install software breakpoints.  KGDB
> uses a special (x86-specific) breakpoint type for these kinds of
> breakpoints (BP_POKE_BREAKPOINT).  When removing a breakpoint, KGDB
> always adheres to the breakpoint's original installment method, which is
> determined by its type.
>
> Before this fix, early (non-"poke") breakpoints could not be removed
> after the kernel text was set as read-only since the original code
> patching mechanism was no longer allowed to remove the breakpoints.
> Eventually, this even caused the kernel to hang (loop between int3
> instruction and the function kgdb_skipexception).
>
> With this patch, we convert early breakpoints to "poke" breakpoints
> after the kernel text has been made read-only.  This makes them
> removable later.

Please check Documentation/process/ including maintainers.tip for change
log rules.

But aside of that why having this BP_TYPE dance in the first place?

kgdb_arch_set_breakpoint(...)
{
        if (system_state == SYSTEM_BOOTING) {
        	text_poke_early(...);
                return;
        }
        if (mutex_is_locked(&text_mutex))
        	return -EBUSY;
	text_poke_kgdb(...);
}

See? No breakpoint type, no magic post readonly fixup, nothing.

Similar for arch_remove_breakpoint(). I reply to that gem on the other
patch.

Thanks,

        tglx