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

On Mon, 25 Aug 2025 09:18:53 +0800 Coiby Xu [off-list ref] wrote:

quoted

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?


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 <redacted>
Cc: Coiby Xu <redacted>
Cc: "Daniel P. Berrange" <redacted>
Cc: Dave Hansen <redacted>
Cc: Dave Young <redacted>
Cc: Kairui Song <redacted>
Cc: Liu Pingfan <redacted>
Cc: Milan Broz <redacted>
Cc: Ondrej Kozina <redacted>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: <redacted>
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;

_