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

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Message-ID: <alpine.DEB.2.20.1707041643400.9000@nanos>
Date:   Tue, 4 Jul 2017 16:46:58 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Baoquan He <bhe@...hat.com>
cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
        Kees Cook <keescook@...omium.org>, thgarnie@...gle.com,
        caoj.fnst@...fujitsu.com, izumi.taku@...fujitsu.com,
        Matt Fleming <matt@...eblueprint.co.uk>
Subject: Re: [PATCH v2 2/2] x86/boot/KASLR: Restrict kernel to be randomized
 in mirror regions

On Tue, 4 Jul 2017, Baoquan He wrote:

> 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.

The pointer is not NULL, it's not initialized.
 
> 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

Indeed. Matt?

Thanks,

	tglx