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Date:   Tue, 8 Jan 2019 16:46:57 +0800
From:   Dave Young <dyoung@redhat.com>
To:     Baoquan He <bhe@redhat.com>
Cc:     linux-kernel@vger.kernel.org, kexec@lists.infradead.org,
        AKASHI Takahiro <takahiro.akashi@linaro.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Eric W. Biederman" <ebiederm@xmission.com>, x86@kernel.org,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vivek Goyal <vgoyal@redhat.com>
Subject: Re: [PATCH V2] x86/kexec: fix a kexec_file_load failure
Message-ID: <20190108084657.GA32321@dhcp-128-65.nay.redhat.com>
References: <20181228011247.GA9999@dhcp-128-65.nay.redhat.com>
 <20190108052440.GA17983@MiWiFi-R3L-srv>
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On 01/08/19 at 01:24pm, Baoquan He wrote:
> 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@redhat.com>
> > Cc: <stable@vger.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?

C designated initializers will make sure to initialize it as zero.
We set KEXEC_BUF_MEM_UNKNOWN as 0 so it just works.

> 
> 	/* 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
> > 

Thanks
Dave