LKML Archive on lore.kernel.org
 help / color / Atom feed
From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Borislav Petkov <bp@alien8.de>
Cc: "Gustavo A. R. Silva" <gustavo@embeddedor.com>,
	tglx@linutronix.de, hpa@zytor.com, linux-kernel@vger.kernel.org,
	mingo@redhat.com, x86@kernel.org, mingo@kernel.org,
	kirill.shutemov@linux.intel.com,
	linux-tip-commits@vger.kernel.org
Subject: Re: [tip:x86/urgent] x86/boot/compressed/64: Fix boot on machines with broken E820 table
Date: Mon, 26 Aug 2019 16:33:26 +0300
Message-ID: <20190826133326.7cxb4vbmiawffv2r@box> (raw)
In-Reply-To: <20190826071539.GB27636@zn.tnic>

On Mon, Aug 26, 2019 at 09:15:39AM +0200, Borislav Petkov wrote:
> On Sun, Aug 25, 2019 at 10:33:15PM -0500, Gustavo A. R. Silva wrote:
> > Hi all,
> > 
> > On 8/19/19 9:16 AM, tip-bot for Kirill A. Shutemov wrote:
> > [..]
> > > 
> > > diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c
> > > index 5f2d03067ae5..2faddeb0398a 100644
> > > --- a/arch/x86/boot/compressed/pgtable_64.c
> > > +++ b/arch/x86/boot/compressed/pgtable_64.c
> > > @@ -72,6 +72,8 @@ static unsigned long find_trampoline_placement(void)
> > >  
> > >  	/* Find the first usable memory region under bios_start. */
> > >  	for (i = boot_params->e820_entries - 1; i >= 0; i--) {
> > > +		unsigned long new;
> > > +
> > >  		entry = &boot_params->e820_table[i];
> > >  
> > >  		/* Skip all entries above bios_start. */
> > > @@ -84,15 +86,20 @@ static unsigned long find_trampoline_placement(void)
> > >  
> > >  		/* Adjust bios_start to the end of the entry if needed. */
> > >  		if (bios_start > entry->addr + entry->size)
> > 
> > Notice that if this condition happens to be false, we end up with an
> > uninitialized variable *new*.
> 
> Yap, good catch.

:facepalm:

> > What would be the right value to assign to *new* at declaration under
> > this condition?
> 
> Looking at the changed flow of the loop, how we use new instead of
> bios_start and how we assign new back to bios_start, I think we should
> do:
> 
> 		unsigned long new = bios_start;
> 
> at the beginning...

Right.

What about this:

From b613c675e6690ef5608a5abf71d90e15ced31b2b Mon Sep 17 00:00:00 2001
From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Date: Mon, 26 Aug 2019 16:26:01 +0300
Subject: [PATCH] x86/boot/compressed/64: Fix missining initialization in
 find_trampoline_placement()

Gustavo noticed that 'new' can be left uninitialized if 'bios_start'
happens to be less or equal to 'entry->addr + entry->size'.

Initialize the variable at the start of the iteration to current value
of 'bios_start'.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Fixes: 0a46fff2f910 ("x86/boot/compressed/64: Fix boot on machines with broken E820 table")
---
 arch/x86/boot/compressed/pgtable_64.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c
index 2faddeb0398a..c8862696a47b 100644
--- a/arch/x86/boot/compressed/pgtable_64.c
+++ b/arch/x86/boot/compressed/pgtable_64.c
@@ -72,7 +72,7 @@ static unsigned long find_trampoline_placement(void)
 
 	/* Find the first usable memory region under bios_start. */
 	for (i = boot_params->e820_entries - 1; i >= 0; i--) {
-		unsigned long new;
+		unsigned long new = bios_start;
 
 		entry = &boot_params->e820_table[i];
 
-- 
 Kirill A. Shutemov

      reply index

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-13 13:16 [PATCH] " Kirill A. Shutemov
2019-08-19 14:16 ` [tip:x86/urgent] " tip-bot for Kirill A. Shutemov
2019-08-26  3:33   ` Gustavo A. R. Silva
2019-08-26  7:15     ` Borislav Petkov
2019-08-26 13:33       ` Kirill A. Shutemov [this message]

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20190826133326.7cxb4vbmiawffv2r@box \
    --to=kirill@shutemov.name \
    --cc=bp@alien8.de \
    --cc=gustavo@embeddedor.com \
    --cc=hpa@zytor.com \
    --cc=kirill.shutemov@linux.intel.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-tip-commits@vger.kernel.org \
    --cc=mingo@kernel.org \
    --cc=mingo@redhat.com \
    --cc=tglx@linutronix.de \
    --cc=x86@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org linux-kernel@archiver.kernel.org
	public-inbox-index lkml


Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/ public-inbox