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

[Andrew Morton]

On Mon, 25 Aug 2025 09:18:53 +0800 Coiby Xu <coxu@xxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxx? 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?


From: Breno Leitao <leitao@xxxxxxxxxx>
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@xxxxxxxxxx>
Cc: Baoquan He <bhe@xxxxxxxxxx>
Cc: Coiby Xu <coxu@xxxxxxxxxx>
Cc: "Daniel P. Berrange" <berrange@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Dave Young <dyoung@xxxxxxxxxx>
Cc: Kairui Song <ryncsn@xxxxxxxxx>
Cc: Liu Pingfan <kernelfans@xxxxxxxxx>
Cc: Milan Broz <gmazyland@xxxxxxxxx>
Cc: Ondrej Kozina <okozina@xxxxxxxxxx>
Cc: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 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;
_