linux-kernel - Re: [PATCH] arm64: kernel: initialize missing kexec

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Message-ID: <aSmSmH5-8iXOErKw@willie-the-truck>
Date: Fri, 28 Nov 2025 12:16:24 +0000
From: Will Deacon <will@...nel.org>
To: Yeoreum Yun <yeoreum.yun@....com>
Cc: catalin.marinas@....com, akpm@...ux-foundation.org, bhe@...hat.com,
	leitao@...ian.org, coxu@...hat.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: kernel: initialize missing kexec_buf->random field

On Thu, Nov 27, 2025 at 06:26:44PM +0000, Yeoreum Yun wrote:
> Commit bf454ec31add ("kexec_file: allow to place kexec_buf randomly")
> introduced the kexec_buf->random field to enable random placement of
> kexec_buf.
> 
> However, this field was never properly initialized for kexec images
> that do not need to be placed randomly, leading to the following UBSAN
> warning:
> 
> [  +0.364528] ------------[ cut here ]------------
> [  +0.000019] UBSAN: invalid-load in ./include/linux/kexec.h:210:12
> [  +0.000131] load of value 2 is not a valid value for type 'bool' (aka '_Bool')
> [  +0.000003] CPU: 4 UID: 0 PID: 927 Comm: kexec Not tainted 6.18.0-rc7+ #3 PREEMPT(full)
> [  +0.000002] Hardware name: QEMU QEMU Virtual Machine, BIOS 0.0.0 02/06/2015
> [  +0.000000] Call trace:
> [  +0.000001]  show_stack+0x24/0x40 (C)
> [  +0.000006]  __dump_stack+0x28/0x48
> [  +0.000002]  dump_stack_lvl+0x7c/0xb0
> [  +0.000002]  dump_stack+0x18/0x34
> [  +0.000001]  ubsan_epilogue+0x10/0x50
> [  +0.000002]  __ubsan_handle_load_invalid_value+0xc8/0xd0
> [  +0.000003]  locate_mem_hole_callback+0x28c/0x2a0
> [  +0.000003]  kexec_locate_mem_hole+0xf4/0x2f0
> [  +0.000001]  kexec_add_buffer+0xa8/0x178
> [  +0.000002]  image_load+0xf0/0x258
> [  +0.000001]  __arm64_sys_kexec_file_load+0x510/0x718
> [  +0.000002]  invoke_syscall+0x68/0xe8
> [  +0.000001]  el0_svc_common+0xb0/0xf8
> [  +0.000002]  do_el0_svc+0x28/0x48
> [  +0.000001]  el0_svc+0x40/0xe8
> [  +0.000002]  el0t_64_sync_handler+0x84/0x140
> [  +0.000002]  el0t_64_sync+0x1bc/0x1c0
> 
> To address this, initialise kexec_buf->random field properly.
> 
> Fixes: bf454ec31add ("kexec_file: allow to place kexec_buf randomly")
> Signed-off-by: Yeoreum Yun <yeoreum.yun@....com>
> ---
>  arch/arm64/kernel/kexec_image.c        | 3 +++
>  arch/arm64/kernel/machine_kexec_file.c | 6 +++++-
>  2 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kernel/kexec_image.c b/arch/arm64/kernel/kexec_image.c
> index 532d72ea42ee..db6fb8c599a1 100644
> --- a/arch/arm64/kernel/kexec_image.c
> +++ b/arch/arm64/kernel/kexec_image.c
> @@ -76,6 +76,9 @@ static void *image_load(struct kimage *image,
>  	kbuf.buf_min = 0;
>  	kbuf.buf_max = ULONG_MAX;
>  	kbuf.top_down = false;
> +#ifdef CONFIG_CRASH_DUMP
> +	kbuf.random = false;
> +#endif
> 
>  	kbuf.buffer = kernel;
>  	kbuf.bufsz = kernel_len;
> diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c
> index 410060ebd86d..06f38866424a 100644
> --- a/arch/arm64/kernel/machine_kexec_file.c
> +++ b/arch/arm64/kernel/machine_kexec_file.c
> @@ -94,7 +94,11 @@ int load_other_segments(struct kimage *image,
>  			char *initrd, unsigned long initrd_len,
>  			char *cmdline)
>  {
> -	struct kexec_buf kbuf = {};
> +	struct kexec_buf kbuf = {
> +#ifdef CONFIG_CRASH_DUMP
> +		.random = false,
> +#endif
> +	};

This hunk is pointless.

Will