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From: Josh Poimboeuf <jpoimboe@kernel.org>
To: Juergen Gross <jgross@suse.com>
Cc: xen-devel@lists.xenproject.org, x86@kernel.org,
	linux-kernel@vger.kernel.org,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH v2 2/3] x86: fix setup of brk area
Date: Wed, 29 Jun 2022 10:14:57 -0700	[thread overview]
Message-ID: <20220629171457.amdsrgaxady55hds@treble> (raw)
In-Reply-To: <20220623094608.7294-3-jgross@suse.com>

Hi Juergen,

It helps to actually Cc the person who broke it ;-)

On Thu, Jun 23, 2022 at 11:46:07AM +0200, Juergen Gross wrote:
> Commit e32683c6f7d2 ("x86/mm: Fix RESERVE_BRK() for older binutils")
> put the brk area into the .bss..brk section (placed directly behind
> .bss),

Hm? It didn't actually do that.

For individual translation units, it did rename the section from
".brk_reservation" to ".bss..brk".  But then during linking it's still
placed in .brk in vmlinux, just like before.

> causing it not to be cleared initially. As the brk area is used
> to allocate early page tables, these might contain garbage in not
> explicitly written entries.
> 
> This is especially a problem for Xen PV guests, as the hypervisor will
> validate page tables (check for writable page tables and hypervisor
> private bits) before accepting them to be used. There have been reports
> of early crashes of PV guests due to illegal page table contents.
> 
> Fix that by letting clear_bss() clear the brk area, too.

While it does make sense to clear the brk area, I don't understand how
my patch broke this.  How was it getting cleared before?

-- 
Josh

  reply	other threads:[~2022-06-29 17:15 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-06-23  9:46 [PATCH v2 0/3] x86: fix brk area initialization Juergen Gross
2022-06-23  9:46 ` [PATCH v2 1/3] x86/xen: use clear_bss() for Xen PV guests Juergen Gross
2022-06-23  9:51   ` Jan Beulich
2022-06-28 12:03     ` Juergen Gross
2022-06-23  9:46 ` [PATCH v2 2/3] x86: fix setup of brk area Juergen Gross
2022-06-29 17:14   ` Josh Poimboeuf [this message]
2022-06-30  6:55     ` Juergen Gross
2022-06-23  9:46 ` [PATCH v2 3/3] x86: fix .brk attribute in linker script Juergen Gross
2022-06-29 17:18   ` Josh Poimboeuf
2022-06-29 14:10 ` [PATCH v2 0/3] x86: fix brk area initialization Juergen Gross
2022-06-29 17:17   ` Boris Ostrovsky
2022-07-05 11:14   ` Thorsten Leemhuis

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