linux-kernel - Re: [PATCH v2 2/2] x86/boot/KASLR: Restrict kernel to be randomized in mirror regions

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Date:   Tue, 4 Jul 2017 22:30:34 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, hpa@...or.com,
        mingo@...nel.org, keescook@...omium.org, thgarnie@...gle.com,
        caoj.fnst@...fujitsu.com, izumi.taku@...fujitsu.com
Subject: Re: [PATCH v2 2/2] x86/boot/KASLR: Restrict kernel to be randomized
 in mirror regions

On 07/04/17 at 04:00pm, Thomas Gleixner wrote:
> On Tue, 4 Jul 2017, Baoquan He wrote:
> > +/* Marks if efi mirror regions have been found and handled. */
> > +static bool efi_mirror_found;
> > +
> > +static void process_efi_entry(unsigned long minimum, unsigned long image_size)
> > +{
> > +	struct efi_info *e = &boot_params->efi_info;
> > +	struct mem_vector region;
> > +	efi_memory_desc_t *md;
> > +	unsigned long pmap;
> > +	char *signature;
> > +	u32 nr_desc;
> > +	int i;
> > +
> > +
> > +#ifdef CONFIG_EFI
> > +	signature = (char *)&boot_params->efi_info.efi_loader_signature;
> > +#endif
> 
> So if CONFIG_EFI=n you happily dereference the uninitialized signature
> pointer ...

Right, this is a mistake. Thanks for pointing it out. I should have
checked if the pointer is NULL.

In fact I just referred to code in setup_arch(). Now I have a question,
though CONFIG_EFI=y but efi firmware is not enabled,
boot_params.efi_info.efi_loader_signature should be initilized to 0.
Then below code is also problematic.

#ifdef CONFIG_EFI
        if (!strncmp((char *)&boot_params.efi_info.efi_loader_signature,                                                                         
                     EFI32_LOADER_SIGNATURE, 4)) {
                set_bit(EFI_BOOT, &efi.flags);
        } else if (!strncmp((char *)&boot_params.efi_info.efi_loader_signature,
                     EFI64_LOADER_SIGNATURE, 4)) {
                set_bit(EFI_BOOT, &efi.flags);
                set_bit(EFI_64BIT, &efi.flags);
        }

        if (efi_enabled(EFI_BOOT))
                efi_memblock_x86_reserve_range();
#endif

> 
> Why is process_efi_entry() invoked at all if EFI is not enabled?


Yeah, and it's better to check if CONFIG_EFI is enabled before
invocation of process_efi_entry(). Let me change it as below and repost.
Thanks again for looking into this patchset.

+#ifdef CONFIG_EFI
        process_efi_entry(minimum, image_size);
+#endif

> 
> > +	if (strncmp(signature, EFI32_LOADER_SIGNATURE, 4) &&
> > +	    strncmp(signature, EFI64_LOADER_SIGNATURE, 4))
> > +		return;
> > +
> 
> Thanks,
> 
> 	tglx