Re: [PATCH v3 3/4] add kexec_cmdline used to ima

Mimi Zohar
2019-05-02T16:52:55Z

On Mon, 2019-04-29 at 14:47 -0700, Prakhar Srivastava wrote:
> From: Prakhar Srivastava <prsriva02@gmail.com>
>
> prepend the kernel file name to kexec_cmdline
> before measuring the buffer.
>

kexec doesn't really know or care about IMA.  Other than the IMA call,
itself, nothing should be added to kexec files.  As mentioned in 1/4,
the IMA hook would be named something like ima_kexec_cmdline().

Mimi

> Signed-off-by: Prakhar Srivastava <prsriva02@gmail.com>
> ---
> kernel/kexec_core.c | 57 +++++++++++++++++++++++++++++++++++++++++++++
> kernel/kexec_file.c | 14 +++++++++++
> 2 files changed, 71 insertions(+)
>
> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> index d7140447be75..4667f03d406e 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -1213,3 +1213,60 @@ void __weak arch_kexec_protect_crashkres(void)
>
> void __weak arch_kexec_unprotect_crashkres(void)
> {}
> +
> +/**
> + * kexec_cmdline_prepend_img_name - prepare the buffer with cmdline
> + * that needs to be measured
> + * @outbuf - out buffer that contains the formated string
> + * @kernel_fd - the file identifier for the kerenel image
> + * @cmdline_ptr - ptr to the cmdline buffer
> + * @cmdline_len - len of the buffer.
> + *
> + * This generates a buffer in the format Kerenelfilename::cmdline
> + *
> + * On success return 0.
> + * On failure return -EINVAL.
> + */
> +int kexec_cmdline_prepend_img_name(char **outbuf, int kernel_fd,
> + const char *cmdline_ptr,
> + unsigned long cmdline_len)
> +{
> + int ret = -EINVAL;
> + struct fd f = {};
> + int size = 0;
> + char *buf = NULL;
> + char delimiter[] = "::";
> +
> + if (!outbuf || !cmdline_ptr)
> + goto out;
> +
> + f = fdget(kernel_fd);
> + if (!f.file)
> + goto out;
> +
> + size = (f.file->f_path.dentry->d_name.len + cmdline_len - 1+
> + ARRAY_SIZE(delimiter)) - 1;
> +
> + buf = kzalloc(size, GFP_KERNEL);
> + if (!buf)
> + goto out;
> +
> + memcpy(buf, f.file->f_path.dentry->d_name.name,
> + f.file->f_path.dentry->d_name.len);
> + memcpy(buf + f.file->f_path.dentry->d_name.len,
> + delimiter, ARRAY_SIZE(delimiter) - 1);
> + memcpy(buf + f.file->f_path.dentry->d_name.len +
> + ARRAY_SIZE(delimiter) - 1,
> + cmdline_ptr, cmdline_len - 1);
> +
> + *outbuf = buf;
> + ret = size;
> +
> + pr_debug("kexec cmdline buff: %s\n", buf);
> +
> +out:
> + if (f.file)
> + fdput(f);
> +
> + return ret;
> +}
> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> index f1d0e00a3971..d287e139085c 100644
> --- a/kernel/kexec_file.c
> +++ b/kernel/kexec_file.c
> @@ -191,6 +191,8 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,
> int ret = 0;
> void *ldata;
> loff_t size;
> + char *buff_to_measure = NULL;
> + int buff_to_measure_size = 0;
>
> ret = kernel_read_file_from_fd(kernel_fd, &image->kernel_buf,
> &size, INT_MAX, READING_KEXEC_IMAGE);
> @@ -241,6 +243,16 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,
> ret = -EINVAL;
> goto out;
> }
> +
> + /* IMA measures the cmdline args passed to the next kernel*/
> + buff_to_measure_size =
> + kexec_cmdline_prepend_img_name(&buff_to_measure,
> + kernel_fd, image->cmdline_buf, image->cmdline_buf_len);
> +
> + ima_buffer_check(buff_to_measure, buff_to_measure_size,
> + "kexec_cmdline");
> +
> +
> }
>
> /* Call arch image load handlers */
> @@ -253,7 +265,9 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,
>
> image->image_loader_data = ldata;
> out:
> +
> /* In case of error, free up all allocated memory in this function */
> + kfree(buff_to_measure);
> if (ret)
> kimage_file_post_load_cleanup(image);
> return ret;