Re: [PATCH v9 1/8] kexec_file: allow to place kexec_buf randomly
From: Coiby Xu <hidden>
Date: 2025-08-25 01:21:01
Also in:
kexec, lkml
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:quoted
+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!
quoted hunk ↗ jump to hunk
I am wondering if we should have something like , while the support for arm64 is not done: commit 2608bd8c26b62a9a7cc50106e93d3a1ffb1e1188 Author: Breno Leitao [off-list ref] 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 [off-list ref]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