linux-kernel - Re: [PATCH v9 1/8] kexec_file: allow to place kexec

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Message-Id: <20250825180531.94bfb86a26a43127c0a1296f@linux-foundation.org>
Date: Mon, 25 Aug 2025 18:05:31 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Coiby Xu <coxu@...hat.com>
Cc: Breno Leitao <leitao@...ian.org>, kexec@...ts.infradead.org, Ondrej
 Kozina <okozina@...hat.com>, Milan Broz <gmazyland@...il.com>, Thomas
 Staudt <tstaudt@...ibm.com>, Daniel P . Berrangé
 <berrange@...hat.com>, Kairui Song <ryncsn@...il.com>, Pingfan Liu
 <kernelfans@...il.com>, Baoquan He <bhe@...hat.com>, Dave Young
 <dyoung@...hat.com>, linux-kernel@...r.kernel.org, x86@...nel.org, Dave
 Hansen <dave.hansen@...el.com>, Vitaly Kuznetsov <vkuznets@...hat.com>,
 Arnaud Lefebvre <arnaud.lefebvre@...ver-cloud.com>, Jan Pazdziora
 <jpazdziora@...hat.com>, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v9 1/8] kexec_file: allow to place kexec_buf randomly

On Mon, 25 Aug 2025 09:18:53 +0800 Coiby Xu <coxu@...hat.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@...ts.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?

From: Breno Leitao <leitao@...ian.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@...ian.org>
Cc: Baoquan He <bhe@...hat.com>
Cc: Coiby Xu <coxu@...hat.com>
Cc: "Daniel P. Berrange" <berrange@...hat.com>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: Dave Young <dyoung@...hat.com>
Cc: Kairui Song <ryncsn@...il.com>
Cc: Liu Pingfan <kernelfans@...il.com>
Cc: Milan Broz <gmazyland@...il.com>
Cc: Ondrej Kozina <okozina@...hat.com>
Cc: Vitaly Kuznetsov <vkuznets@...hat.com>
Cc: <stable@...r.kernel.org>
Signed-off-by: Andrew Morton <akpm@...ux-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;
_