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@xxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxx>
Reported-by: "Gustavo A. R. Silva" <gustavo@xxxxxxxxxxxxxx>
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
|