linux-kernel - Re: [PATCH v2 2/2] kexec_file: Increase maximum file size to 4G

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Date:   Mon, 6 Jun 2022 10:56:25 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Pasha Tatashin <pasha.tatashin@...een.com>
Cc:     sashal@...nel.org, ebiederm@...ssion.com, rburanyi@...gle.com,
        gthelen@...gle.com, viro@...iv.linux.org.uk,
        kexec@...ts.infradead.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] kexec_file: Increase maximum file size to 4G

On 05/27/22 at 02:55am, Pasha Tatashin wrote:
> In some case initrd can be large. For example, it could be a netboot
> image loaded by u-root, that is kexec'ing into it.
> 
> The maximum size of initrd is arbitrary set to 2G. Also, the limit is
> not very obvious because it is hidden behind a generic INT_MAX macro.
> 
> Theoretically, we could make it LONG_MAX, but it is safer to keep it
> sane, and just increase it to 4G.

Do we need to care about 32bit system where initramfs could be larger
than 2G? On 32bit system, SSIZE_MAX is still 2G, right?

Another concern is if 2G is enough. If we can foresee it might need be
enlarged again in a near future, LONG_MAX certainly is not a good
value, but a little bigger multiple of 2G can be better?

> 
> Increase the size to 4G, and make it obvious by having a new macro
> that specifies the maximum file size supported by kexec_file_load()
> syscall: KEXEC_FILE_SIZE_MAX.
> 
> Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
> ---
>  kernel/kexec_file.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> index 8347fc158d2b..f00cf70d82b9 100644
> --- a/kernel/kexec_file.c
> +++ b/kernel/kexec_file.c
> @@ -31,6 +31,9 @@
>  
>  static int kexec_calculate_store_digests(struct kimage *image);
>  
> +/* Maximum size in bytes for kernel/initrd files. */
> +#define KEXEC_FILE_SIZE_MAX	min_t(s64, 4LL << 30, SSIZE_MAX)
> +
>  /*
>   * Currently this is the only default function that is exported as some
>   * architectures need it to do additional handlings.
> @@ -223,11 +226,12 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,
>  			     const char __user *cmdline_ptr,
>  			     unsigned long cmdline_len, unsigned flags)
>  {
> -	int ret;
> +	ssize_t ret;
>  	void *ldata;
>  
>  	ret = kernel_read_file_from_fd(kernel_fd, 0, &image->kernel_buf,
> -				       INT_MAX, NULL, READING_KEXEC_IMAGE);
> +				       KEXEC_FILE_SIZE_MAX, NULL,
> +				       READING_KEXEC_IMAGE);
>  	if (ret < 0)
>  		return ret;
>  	image->kernel_buf_len = ret;
> @@ -247,7 +251,7 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,
>  	/* It is possible that there no initramfs is being loaded */
>  	if (!(flags & KEXEC_FILE_NO_INITRAMFS)) {
>  		ret = kernel_read_file_from_fd(initrd_fd, 0, &image->initrd_buf,
> -					       INT_MAX, NULL,
> +					       KEXEC_FILE_SIZE_MAX, NULL,
>  					       READING_KEXEC_INITRAMFS);
>  		if (ret < 0)
>  			goto out;
> -- 
> 2.36.1.124.g0e6072fb45-goog
>