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

Baoquan He
2022-06-06T02:56:41Z

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@soleen.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
>