Re: [PATCH v9 1/8] kexec_file: allow to place kexec_buf randomly

[Baoquan He <bhe@redhat.com>]

On 08/25/25 at 06:05pm, Andrew Morton wrote:
> On Mon, 25 Aug 2025 09:18:53 +0800 Coiby Xu <coxu@redhat.com> wrote:
> 
> > >diff --git a/arch/arm64/kernel/kexec_image.c b/arch/arm64/kernel/kexec_image.c
> > >index 532d72ea42ee8..287b25e674d76 100644
> > >--- a/arch/arm64/kernel/kexec_image.c
> > >+++ b/arch/arm64/kernel/kexec_image.c
> > >@@ -76,6 +76,7 @@ static void *image_load(struct kimage *image,
> > > 	kbuf.buf_min = 0;
> > > 	kbuf.buf_max = ULONG_MAX;
> > > 	kbuf.top_down = false;
> > >+	kbuf.random = 0;
> > >
> > > 	kbuf.buffer = kernel;
> > > 	kbuf.bufsz = kernel_len;
> > >
> > 
> > And also thanks for posing a fix! The patch LGTM. Can you add a Fixes
> > tag 'Fixes: bf454ec31add ("kexec_file: allow to place kexec_buf
> > randomly")' and then send it to kexec@lists.infradead.org? Thanks!
> 
> I turned all this into a regular patch and queued it (see below),
> thanks.  No additional actions are needed.
> 
> I'm really not liking that code.  I laboriously verified that all
> fields of kexec_buf are now initialized, except for `cma'.  Is that a
> bug?
> 
> This function has a call frequency of about 3x per week.  Can we please
> just memset the whole thing so people don't have to worry about this
> any more?

Yeah, adding these trivial patches to mute XXSAN warning is annoying.
Maybe arm64 can initialize the local variable kbuf like we do in x86_64
as below, to explicitly set the necessary fields when defining.

static void *bzImage64_load(struct kimage *image, char *kernel,
                            unsigned long kernel_len, char *initrd,
                            unsigned long initrd_len, char *cmdline,
                            unsigned long cmdline_len)
{
......
        struct kexec_buf kbuf = { .image = image, .buf_max = ULONG_MAX,
                                  .top_down = true };
        struct kexec_buf pbuf = { .image = image, .buf_min = MIN_PURGATORY_ADDR,
                                  .buf_max = ULONG_MAX, .top_down = true };
.....
}

> 
> 
> From: Breno Leitao <leitao@debian.org>
> Subject: kexec/arm64: initialize the random field of kbuf to zero in the image loader
> Date: Thu Aug 21 04:11:21 2025 -0700
> 
> Add an explicit initialization for the random member of the kbuf structure
> within the image_load function in arch/arm64/kernel/kexec_image.c. 
> Setting kbuf.random to zero ensures a deterministic and clean starting
> state for the buffer used during kernel image loading, avoiding this UBSAN
> issue later, when kbuf.random is read.
> 
>   [   32.362488] UBSAN: invalid-load in ./include/linux/kexec.h:210:10
>   [   32.362649] load of value 252 is not a valid value for type '_Bool'
> 
> Link: https://lkml.kernel.org/r/oninomspajhxp4omtdapxnckxydbk2nzmrix7rggmpukpnzadw@c67o7njgdgm3
> Fixes: bf454ec31add ("kexec_file: allow to place kexec_buf randomly
> Signed-off-by: Breno Leitao <leitao@debian.org>
> Cc: Baoquan He <bhe@redhat.com>
> Cc: Coiby Xu <coxu@redhat.com>
> Cc: "Daniel P. Berrange" <berrange@redhat.com>
> Cc: Dave Hansen <dave.hansen@intel.com>
> Cc: Dave Young <dyoung@redhat.com>
> Cc: Kairui Song <ryncsn@gmail.com>
> Cc: Liu Pingfan <kernelfans@gmail.com>
> Cc: Milan Broz <gmazyland@gmail.com>
> Cc: Ondrej Kozina <okozina@redhat.com>
> Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
> 
>  arch/arm64/kernel/kexec_image.c |    1 +
>  1 file changed, 1 insertion(+)
> 
> --- a/arch/arm64/kernel/kexec_image.c~kexec-arm64-initialize-the-random-field-of-kbuf-to-zero-in-the-image-loader
> +++ a/arch/arm64/kernel/kexec_image.c
> @@ -76,6 +76,7 @@ static void *image_load(struct kimage *i
>  	kbuf.buf_min = 0;
>  	kbuf.buf_max = ULONG_MAX;
>  	kbuf.top_down = false;
> +	kbuf.random = 0;
>  
>  	kbuf.buffer = kernel;
>  	kbuf.bufsz = kernel_len;
> _
>