Re: [PATCH] kexec: restore functionality to preserve fd xattrs for uncompressed kernel images

[Simon Horman <horms@kernel.org>]

On Thu, May 07, 2026 at 09:54:17PM +0000, Alejandro Hernandez wrote:
> Since commit 714fa115 xattrs attached to a kernel image file (such as IMA
> signatures) are not being preserved, do_kexec_file_load() was modified to use
> memfd_create() which now passes an anonymous file descriptor to
> kexec_file_load(). This change eliminated the filesystem inode identity of the
> original kernel file, hence attributes are no longer visible to the kernel IMA
> appraisal handler during kexec_file_load, causing IMA policy enforcement to fail
> even for validly signed kernel images.
> 
> This patch attempts to restore such behavior although, only does it for
> uncompressed kernel images. To do this, we first figure out if the image file is
> compressed or not and call each method accordingly.
> 
> Compressed images continue to use memfd and cannot carry forward the original fd
> security attributes, since their decompressed bytes do not match the signed
> artifact. Proper handling of compressed images with IMA would require either
> signing the decompressed artifact or kernel-side support for decompression
> within the kexec_file_load path.
> 
> Signed-off-by: Alejandro Hernandez Samaniego <alhe@linux.microsoft.com>

Hi Alejandro,

Thanks for the patch.

Overall this looks good to me. But I'm wondering if you could spin a v2
to address a minor code-style issue I have noted inline.

> ---
>  kexec/kexec.c | 42 +++++++++++++++++++++++++++++++++++-------
>  1 file changed, 35 insertions(+), 7 deletions(-)
> 
> diff --git a/kexec/kexec.c b/kexec/kexec.c
> index 08edfca..a388762 100644
> --- a/kexec/kexec.c
> +++ b/kexec/kexec.c
> @@ -1328,17 +1328,41 @@ static int do_kexec_file_load(int fileind, int argc, char **argv,
>  
>  	kernel = argv[fileind];
>  
> -	/* slurp in the input kernel */
> +        /* Hold original fd with its xattrs */
> +	kernel_fd = open(kernel, O_RDONLY);
> +	if (kernel_fd == -1) {
> +		fprintf(stderr, "Failed to open file %s:%s\n", kernel,
> +				strerror(errno));
> +		return EFAILED;
> +	}
> +
> +	/* Compressed vs Uncompressed */
> +	struct stat kernel_stat;
> +	off_t kernel_file_size = -1;

I would prefer if we stuck to declaring local variables
at the top of this function.

> +	if (fstat(kernel_fd, &kernel_stat) == 0)
> +		kernel_file_size = kernel_stat.st_size;
> +
> +        /* slurp in the input kernel */
>  	kernel_buf = slurp_decompress_file(kernel, &kernel_size);
>  	if (!kernel_buf) {
>  		fprintf(stderr, "Failed to decompress file %s:%s\n", kernel,
>  				strerror(errno));
> +		close(kernel_fd);
>  		return EFAILED;
>  	}

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