linux-kernel - Re: [PATCH v7 1/7] ima: define and call ima_alloc_kexec_file

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Message-ID: <1a7e9cf84715386b7ac3dc2103fd38ba180dd216.camel@linux.ibm.com>
Date: Fri, 07 Feb 2025 14:10:32 -0500
From: Mimi Zohar <zohar@...ux.ibm.com>
To: steven chen <chenste@...ux.microsoft.com>, stefanb@...ux.ibm.com,
        roberto.sassu@...weicloud.com, roberto.sassu@...wei.com,
        eric.snowberg@...cle.com, ebiederm@...ssion.com, paul@...l-moore.com,
        code@...icks.com, bauermann@...abnow.com,
        linux-integrity@...r.kernel.org, kexec@...ts.infradead.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: madvenka@...ux.microsoft.com, nramas@...ux.microsoft.com,
        James.Bottomley@...senPartnership.com
Subject: Re: [PATCH v7 1/7] ima: define and call ima_alloc_kexec_file_buf

On Mon, 2025-02-03 at 15:20 -0800, steven chen wrote:
> Carrying the IMA measurement list across kexec requires allocating a
> buffer and copying the measurement records.  Separate allocating the
> buffer and copying the measurement records into separate functions in
> order to allocate the buffer at kexec 'load' and copy the measurements
> at kexec 'execute'.
> 
> This patch includes the following changes:
>  - Refactor ima_dump_measurement_list() to move the memory allocation
>    to a separate function ima_alloc_kexec_file_buf() which allocates
>    buffer of size 'kexec_segment_size' at kexec 'load'.
>  - Make the local variable ima_kexec_file in ima_dump_measurement_list()
>    a local static to the file, so that it can be accessed from 
>    ima_alloc_kexec_file_buf(). Compare actual memory required to ensure 
>    there is enough memory for the entire measurement record.
>  - Copy as many measurement events as possible.
>  - Make necessary changes to the function ima_add_kexec_buffer() to call
>    the above two functions.
>  - Compared the memory size allocated with memory size of the entire 
>    measurement record. If there is not enough memory, it will copy as many
>    IMA measurement records as possible, and this situation will result
>    in a failure of remote attestation.
> 
> Author: Tushar Sugandhi <tusharsu@...ux.microsoft.com>
> Reviewed-by: Stefan Berger <stefanb@...ux.ibm.com>
> Suggested-by: Mimi Zohar <zohar@...ux.ibm.com>
> Signed-off-by: Tushar Sugandhi <tusharsu@...ux.microsoft.com>
> Signed-off-by: steven chen <chenste@...ux.microsoft.com>
> ---
>  security/integrity/ima/ima.h       |   1 +
>  security/integrity/ima/ima_kexec.c | 105 +++++++++++++++++++++--------
>  security/integrity/ima/ima_queue.c |   4 +-
>  3 files changed, 80 insertions(+), 30 deletions(-)
> 
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index 3c323ca213d4..447a6eb07c2d 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -274,6 +274,7 @@ bool ima_template_has_modsig(const struct ima_template_desc
> *ima_template);
>  int ima_restore_measurement_entry(struct ima_template_entry *entry);
>  int ima_restore_measurement_list(loff_t bufsize, void *buf);
>  int ima_measurements_show(struct seq_file *m, void *v);
> +int ima_get_binary_runtime_entry_size(struct ima_template_entry *entry);
>  unsigned long ima_get_binary_runtime_size(void);
>  int ima_init_template(void);
>  void ima_init_template_list(void);
> diff --git a/security/integrity/ima/ima_kexec.c
> b/security/integrity/ima/ima_kexec.c
> index 52e00332defe..b60a902460e2 100644
> --- a/security/integrity/ima/ima_kexec.c
> +++ b/security/integrity/ima/ima_kexec.c
> @@ -15,62 +15,99 @@
>  #include "ima.h"
>  
>  #ifdef CONFIG_IMA_KEXEC
> +static struct seq_file ima_kexec_file;
> +
> +static void ima_reset_kexec_file(struct seq_file *sf)
> +{
> +	sf->buf = NULL;
> +	sf->size = 0;
> +	sf->read_pos = 0;
> +	sf->count = 0;
> +}
> +
> +static void ima_free_kexec_file_buf(struct seq_file *sf)
> +{
> +	vfree(sf->buf);
> +	ima_reset_kexec_file(sf);
> +}
> +
> +static int ima_alloc_kexec_file_buf(size_t segment_size)
> +{
> +	/*
> +	 * kexec 'load' may be called multiple times.
> +	 * Free and realloc the buffer only if the segment_size is
> +	 * changed from the previous kexec 'load' call.
> +	 */
> +	if (ima_kexec_file.buf &&
> +		(ima_kexec_file.size == segment_size)) {
> +		goto out;
> +	}

Nice cleanup from v5.  The line doesn't doesn't need to be split.  Both the
parenthesis and the brackets can be removed.

In the future, before posting patches, please use scripts/checkpatch.pl.

CHECK: Unnecessary parentheses around 'ima_kexec_file.size == segment_size'
#82: FILE: security/integrity/ima/ima_kexec.c:41:
+	if (ima_kexec_file.buf &&
+		(ima_kexec_file.size == segment_size)) {

CHECK: Alignment should match open parenthesis
#83: FILE: security/integrity/ima/ima_kexec.c:42:
+	if (ima_kexec_file.buf &&
+		(ima_kexec_file.size == segment_size)) {

Or simply join the two lines.

thanks,

Mimi

> +
> +	ima_free_kexec_file_buf(&ima_kexec_file);
> +
> +	/* segment size can't change between kexec load and execute */
> +	ima_kexec_file.buf = vmalloc(segment_size);
> +	if (!ima_kexec_file.buf)
> +		return -ENOMEM;
> +
> +	ima_kexec_file.size = segment_size;
> +
> +out:
> +	ima_kexec_file.read_pos = 0;
> +	ima_kexec_file.count = sizeof(struct ima_kexec_hdr);	/* reserved space
> */
> +
> +	return 0;
> +}
>