linux-kernel - Re: [PATCH V2] x86/kexec: fix a kexec_file

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Message-ID: <20190108052440.GA17983@MiWiFi-R3L-srv>
Date:   Tue, 8 Jan 2019 13:24:40 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Dave Young <dyoung@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
        AKASHI Takahiro <takahiro.akashi@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>, x86@...nel.org,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH V2] x86/kexec: fix a kexec_file_load failure

On 12/28/18 at 09:12am, Dave Young wrote:
> The code cleanup mentioned in Fixes tag changed the behavior of
> kexec_locate_mem_hole.  The kexec_locate_mem_hole will try to
> allocate free memory only when kbuf.mem is initialized as zero.
> 
> But in x86 kexec_file_load implementation there are a few places
> the kbuf.mem is reused like below:
>   /* kbuf initialized, kbuf.mem = 0 */
>   ...
>   kexec_add_buffer()
>   ...
>   kexec_add_buffer()
> 
>   The second kexec_add_buffer will reuse previous kbuf but not
>   reinitialize the kbuf.mem.
> 
> Thus kexec_file_load failed because the sanity check failed.
> 
> So explictily reset kbuf.mem to fix the issue.
> 
> Fixes: b6664ba42f14 ("s390, kexec_file: drop arch_kexec_mem_walk()")
> Signed-off-by: Dave Young <dyoung@...hat.com>
> Cc: <stable@...r.kernel.org>
> ---
> V1 -> V2: use KEXEC_BUF_MEM_UNKNOWN in code.
>  arch/x86/kernel/crash.c           | 1 +
>  arch/x86/kernel/kexec-bzimage64.c | 2 ++
>  2 files changed, 3 insertions(+)
> 
> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> index f631a3f15587..6b7890c7889b 100644
> --- a/arch/x86/kernel/crash.c
> +++ b/arch/x86/kernel/crash.c
> @@ -469,6 +469,7 @@ int crash_load_segments(struct kimage *image)
>  

Wondering why this place doesn't need the initialization assignment.
Isn't it to assign in all places before kexec_add_buffer() calling?

	/* Add backup segment. */
        if (image->arch.backup_src_sz) { 
	}

>  	kbuf.memsz = kbuf.bufsz;
>  	kbuf.buf_align = ELF_CORE_HEADER_ALIGN;
> +	kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
>  	ret = kexec_add_buffer(&kbuf);
>  	if (ret) {
>  		vfree((void *)image->arch.elf_headers);
> diff --git a/arch/x86/kernel/kexec-bzimage64.c b/arch/x86/kernel/kexec-bzimage64.c
> index 278cd07228dd..0d5efa34f359 100644
> --- a/arch/x86/kernel/kexec-bzimage64.c
> +++ b/arch/x86/kernel/kexec-bzimage64.c
> @@ -434,6 +434,7 @@ static void *bzImage64_load(struct kimage *image, char *kernel,
>  	kbuf.memsz = PAGE_ALIGN(header->init_size);
>  	kbuf.buf_align = header->kernel_alignment;
>  	kbuf.buf_min = MIN_KERNEL_LOAD_ADDR;

Same question for bzImage64_load(), there are three kexec_add_buffer()
calling, I only saw two initialization in this patch.

> +	kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
>  	ret = kexec_add_buffer(&kbuf);
>  	if (ret)
>  		goto out_free_params;
> @@ -448,6 +449,7 @@ static void *bzImage64_load(struct kimage *image, char *kernel,
>  		kbuf.bufsz = kbuf.memsz = initrd_len;
>  		kbuf.buf_align = PAGE_SIZE;
>  		kbuf.buf_min = MIN_INITRD_LOAD_ADDR;
> +		kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
>  		ret = kexec_add_buffer(&kbuf);
>  		if (ret)
>  			goto out_free_params;
> -- 
> 2.17.0
>