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SubjectRe: [PATCH] x86/boot/compressed/64: Fix 'may be used uninitialized' issue
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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@oracle.com>
>> Cc: Kirill A. Shutemov<kirill@shutemov.name>
>> Cc: Thomas Gleixner<tglx@linutronix.de>
>> Cc: Ingo Molnar<mingo@redhat.com>
>> Cc: Borislav Petkov<bp@alien8.de>
>> Cc: "H. Peter Anvin"<hpa@zytor.com>
>> Cc: x86-ml<x86@kernel.org>
>> ---
>> 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

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