linux-kernel - Re: [PATCH] x86, kdump: Fix efi=noruntime NULL pointer dereference

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Message-ID: <20180809042153.GA4377@dhcp-128-65.nay.redhat.com>
Date:   Thu, 9 Aug 2018 12:21:53 +0800
From:   Dave Young <dyoung@...hat.com>
To:     Mike Galbraith <efault@....de>
Cc:     Baoquan He <bhe@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        lkml <linux-kernel@...r.kernel.org>, kexec@...ts.infradead.org
Subject: Re: [PATCH] x86, kdump: Fix efi=noruntime NULL pointer dereference

Hi Mike,

Thanks for the patch!
On 08/08/18 at 04:03pm, Mike Galbraith wrote:
> When booting with efi=noruntime, we call efi_runtime_map_copy() while
> loading the kdump kernel, and trip over a NULL efi.memmap.map.  Avoid
> that and a useless allocation when the only mapping we can use (1:1)
> is not available.

At first glance, efi_get_runtime_map_size should return 0 in case
noruntime.

Also since we are here, would you mind to restructure the bzImage64_load
function, and try to move all efi related code to setup_efi_state()?


setup_boot_parameters(struct kimage *image, struct boot_params *params,
                      unsigned long params_load_addr,
                      unsigned int efi_map_offset, unsigned int efi_map_sz,
                      unsigned int efi_setup_data_offset)
{
[snip]

#ifdef CONFIG_EFI
        /* Setup EFI state */
        setup_efi_state(params, params_load_addr, efi_map_offset, efi_map_sz,
                        efi_setup_data_offset);
#endif

[snip]
}

Currently bzImage64_load prepares the efi_map_offset, efi_map_sz,
 and efi_setup_data_offset and then pass it to setup_boot_parameters and
setup_efi_state.  It should be better to move those efi_* variables to
setup_efi_state().

So we can call setup_efi_state only when efi runtime is enabled.

> 
> Signed-off-by: Mike Galbraith <efault@....de>
> ---
>  arch/x86/kernel/kexec-bzimage64.c |   22 +++++++++++-----------
>  1 file changed, 11 insertions(+), 11 deletions(-)
> 
> --- a/arch/x86/kernel/kexec-bzimage64.c
> +++ b/arch/x86/kernel/kexec-bzimage64.c
> @@ -122,9 +122,6 @@ static int setup_efi_info_memmap(struct
>  	unsigned long efi_map_phys_addr = params_load_addr + efi_map_offset;
>  	struct efi_info *ei = &params->efi_info;
>  
> -	if (!efi_map_sz)
> -		return 0;
> -
>  	efi_runtime_map_copy(efi_map, efi_map_sz);
>  
>  	ei->efi_memmap = efi_map_phys_addr & 0xffffffff;
> @@ -176,7 +173,7 @@ setup_efi_state(struct boot_params *para
>  	 * acpi_rsdp=<addr> on kernel command line to make second kernel boot
>  	 * without efi.
>  	 */
> -	if (efi_enabled(EFI_OLD_MEMMAP))
> +	if (efi_enabled(EFI_OLD_MEMMAP) || !efi_enabled(EFI_MEMMAP))
>  		return 0;
>  
>  	ei->efi_loader_signature = current_ei->efi_loader_signature;
> @@ -338,7 +335,7 @@ static void *bzImage64_load(struct kimag
>  	struct kexec_entry64_regs regs64;
>  	void *stack;
>  	unsigned int setup_hdr_offset = offsetof(struct boot_params, hdr);
> -	unsigned int efi_map_offset, efi_map_sz, efi_setup_data_offset;
> +	unsigned int efi_map_offset = 0, efi_map_sz = 0, efi_setup_data_offset = 0;
>  	struct kexec_buf kbuf = { .image = image, .buf_max = ULONG_MAX,
>  				  .top_down = true };
>  	struct kexec_buf pbuf = { .image = image, .buf_min = MIN_PURGATORY_ADDR,
> @@ -397,19 +394,22 @@ static void *bzImage64_load(struct kimag
>  	 * have to create separate segment for each. Keeps things
>  	 * little bit simple
>  	 */
> -	efi_map_sz = efi_get_runtime_map_size();
>  	params_cmdline_sz = sizeof(struct boot_params) + cmdline_len +
>  				MAX_ELFCOREHDR_STR_LEN;
>  	params_cmdline_sz = ALIGN(params_cmdline_sz, 16);
> -	kbuf.bufsz = params_cmdline_sz + ALIGN(efi_map_sz, 16) +
> -				sizeof(struct setup_data) +
> -				sizeof(struct efi_setup_data);
> +	kbuf.bufsz = params_cmdline_sz + sizeof(struct setup_data);
> +
> +	/* Now add space for the efi stuff if we have a useable 1:1 mapping. */
> +	if (!efi_enabled(EFI_OLD_MEMMAP) && efi_enabled(EFI_MEMMAP)) {
> +		efi_map_sz = efi_get_runtime_map_size();
> +		kbuf.bufsz += ALIGN(efi_map_sz, 16) + sizeof(struct efi_setup_data);
> +		efi_map_offset = params_cmdline_sz;
> +		efi_setup_data_offset = efi_map_offset + ALIGN(efi_map_sz, 16);
> +	}
>  
>  	params = kzalloc(kbuf.bufsz, GFP_KERNEL);
>  	if (!params)
>  		return ERR_PTR(-ENOMEM);
> -	efi_map_offset = params_cmdline_sz;
> -	efi_setup_data_offset = efi_map_offset + ALIGN(efi_map_sz, 16);
>  
>  	/* Copy setup header onto bootparams. Documentation/x86/boot.txt */
>  	setup_header_size = 0x0202 + kernel[0x0201] - setup_hdr_offset;

Thanks
Dave