linux-kernel - Re: [PATCH] x86/pm: Fix false positive kmemleak report in msr_build

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Message-ID: <CAJZ5v0hdA2PUc8cmJtCNxW-nzHdWV+pxnTEeVu_7YHsHZTmFLw@mail.gmail.com>
Date: Thu, 14 Mar 2024 16:55:31 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Dave Hansen <dave.hansen@...el.com>
Cc: Anton Altaparmakov <anton@...era.com>, "Rafael J . Wysocki" <rafael@...nel.org>, Pavel Machek <pavel@....cz>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"H . Peter Anvin" <hpa@...or.com>, Chen Yu <yu.c.chen@...el.com>, 
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, 
	Catalin Marinas <catalin.marinas@....com>, linux-mm@...ck.org, 
	Matthieu Baerts <matthieu.baerts@...sares.net>, 
	Mat Martineau <mathew.j.martineau@...ux.intel.com>, 
	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>, Ingo Molnar <mingo@...nel.org>, linux-pm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] x86/pm: Fix false positive kmemleak report in msr_build_context().

On Thu, Mar 14, 2024 at 4:05 PM Dave Hansen <dave.hansen@...el.com> wrote:
>
> On 3/14/24 07:26, Anton Altaparmakov wrote:
> >  /* image of the saved processor state */
> >  struct saved_context {
> > -     /*
> > -      * On x86_32, all segment registers except gs are saved at kernel
> > -      * entry in pt_regs.
> > -      */
> > -     u16 gs;
> >       unsigned long cr0, cr2, cr3, cr4;
> >       u64 misc_enable;
> >       struct saved_msrs saved_msrs;
> > @@ -27,6 +22,11 @@ struct saved_context {
> >       unsigned long tr;
> >       unsigned long safety;
> >       unsigned long return_address;
> > +     /*
> > +      * On x86_32, all segment registers except gs are saved at kernel
> > +      * entry in pt_regs.
> > +      */
> > +     u16 gs;
> >       bool misc_enable_saved;
> >  } __attribute__((packed));
>
> Isn't this just kinda poking at the symptoms?  This seems to be
> basically the exact same bug as b0b592cf08, just with a different source
> of unaligned structure members.
>
> There's nothing to keep folks from reintroducing these kinds of issues
> and evidently no way to detect when they happen without lengthy reproducers.

This change is fine with me FWIW, but I agree that making it for
kmemleak reasons feels kind of misguided.