On Thu, Aug 21, 2025 at 04:15:53AM -0700, Breno Leitao wrote:
Hello Coiby,
Hi Breno,
On Fri, May 02, 2025 at 09:12:35AM +0800, Coiby Xu wrote:
+static inline void kexec_random_range_start(unsigned long start,
+ unsigned long end,
+ struct kexec_buf *kbuf,
+ unsigned long *temp_start)
+{
+ unsigned short i;
+
+ if (kbuf->random) {
+ get_random_bytes(&i, sizeof(unsigned short));
+ *temp_start = start + (end - start) / USHRT_MAX * i;
+ }
+}
On arm64, I am getting the following UBSAN warning when accessing
kbuf->random:
[ 32.362428] ------------[ cut here ]------------
[ 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'
and line 210 is your `if (kbuf->random)`.
Basically kbuf was not initialized in arm hosts, and probably has
garbage.
Thank for explaining the problem to me!
I am wondering if we should have something like , while the support for arm64 is
not done:
commit 2608bd8c26b62a9a7cc50106e93d3a1ffb1e1188
Author: Breno Leitao <lei...@debian.org>
Date: Thu Aug 21 04:11:21 2025 -0700
Initialize the random field of kbuf to zero in the ARM64 kexec image loader
Ads 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'
Signed-off-by: Breno Leitao <lei...@debian.org>
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!
--
Best regards,
Coiby
