Re: [PATCH] arm64: kexec: Initialize kexec_buf struct in image_load()

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 26 Aug 2025 05:08:51 -0700 Breno Leitao <leitao@debian.org> wrote:

> The kexec_buf structure was previously declared without initialization
> in image_load(). This led to a UBSAN warning when the structure was
> expanded and uninitialized fields were accessed [1].
> 
> Zero-initializing kexec_buf at declaration ensures all fields are
> cleanly set, preventing future instances of uninitialized memory being
> used.
> 
> Andrew Morton suggested that this function is only called 3x a week[2],
> thus, the memset() cost is inexpressive.
> 

Thanks, I queued this as a replacement for your eralier "kexec/arm64:
initialize the random field of kbuf to zero in the image loader".  I
added cc:stable, a mention of the UBSAN failure and I added thie Fixes:



From: Breno Leitao <leitao@debian.org>
Subject: arm64: kexec: Initialize kexec_buf struct in image_load()
Date: Tue, 26 Aug 2025 05:08:51 -0700

The kexec_buf structure was previously declared without initialization in
image_load().  This led to a UBSAN warning when the structure was expanded
and uninitialized fields were accessed [1].

Zero-initializing kexec_buf at declaration ensures all fields are cleanly
set, preventing future instances of uninitialized memory being used.

Fixes this UBSAN warning:

  [   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'

Andrew Morton suggested that this function is only called 3x a week[2],
thus, the memset() cost is inexpensive.

Link: https://lore.kernel.org/all/oninomspajhxp4omtdapxnckxydbk2nzmrix7rggmpukpnzadw@c67o7njgdgm3/ [1]
Link: https://lore.kernel.org/all/20250825180531.94bfb86a26a43127c0a1296f@linux-foundation.org/ [2]
Link: https://lkml.kernel.org/r/20250826-akpm-v1-1-3c831f0e3799@debian.org
Fixes: bf454ec31add ("kexec_file: allow to place kexec_buf randomly")
Signed-off-by: Breno Leitao <leitao@debian.org>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Mark Rutland <mark.rutland@arm.com>
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 |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/arm64/kernel/kexec_image.c~arm64-kexec-initialize-kexec_buf-struct-in-image_load
+++ a/arch/arm64/kernel/kexec_image.c
@@ -41,7 +41,7 @@ static void *image_load(struct kimage *i
 	struct arm64_image_header *h;
 	u64 flags, value;
 	bool be_image, be_kernel;
-	struct kexec_buf kbuf;
+	struct kexec_buf kbuf = {};
 	unsigned long text_offset, kernel_segment_number;
 	struct kexec_segment *kernel_segment;
 	int ret;
_