Re: [PATCH] x86/boot/compressed/64: Fix 'may be used uninitialized' issue

[Zhenzhong Duan]

On 2019/9/2 17:35, Borislav Petkov wrote:
> On Mon, Sep 02, 2019 at 05:30:24PM +0800, Zhenzhong Duan wrote:
> > Builds kernel with "make bzImage EXTRA_CFLAGS=-Wall", gcc complains:
> >
> > arch/x86/boot/compressed/pgtable_64.c: In function 'paging_prepare':
> > arch/x86/boot/compressed/pgtable_64.c:92:7: warning: 'new' may be used uninitialized in this function [-Wmaybe-uninitialized]
> >     new = round_down(new, PAGE_SIZE);
> >
> > In theory a random value of variable new may pass all the check and be
> > assigned to bios_start, fixing it by assigning it an initial value.
> >
> > Fixes: 0a46fff2f910 ("x86/boot/compressed/64: Fix boot on machines with broken E820 table")
> > Signed-off-by: Zhenzhong Duan<zhenzhong.duan@xxxxxxxxxx>
> > Cc: Kirill A. Shutemov<kirill@xxxxxxxxxxxxx>
> > Cc: Thomas Gleixner<tglx@xxxxxxxxxxxxx>
> > Cc: Ingo Molnar<mingo@xxxxxxxxxx>
> > Cc: Borislav Petkov<bp@xxxxxxxxx>
> > Cc: "H. Peter Anvin"<hpa@xxxxxxxxx>
> > Cc: x86-ml<x86@xxxxxxxxxx>
> > ---
> >   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 2faddeb..c886269 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];
> >   
> > --
> https://git.kernel.org/tip/c96e8483cb2da6695c8b8d0896fe7ae272a07b54
>
> In the future, use tip/master when preparing fixes because it has the
> latest state of the x86 tree and you won't have to duplicate effort,
> like in this case.

Ok, I see. Thanks for your suggestion.

Zhenzhong