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[PATCH v5 1/7] kexec_file: allow to place kexec_buf randomly

Coiby Xu posted 7 patches 1 year, 8 months ago
There is a newer version of this series
[PATCH v5 1/7] kexec_file: allow to place kexec_buf randomly
Posted by Coiby Xu 1 year, 8 months ago 
Currently, kexec_buf is placed in order which means for the same
machine, the info in the kexec_buf is always located at the same
position each time the machine is booted. This may cause a risk for
sensitive information like LUKS volume key. Now struct kexec_buf has a
new field random which indicates it's supposed to be placed in a random
position.

Suggested-by: Jan Pazdziora <jpazdziora@redhat.com>
Signed-off-by: Coiby Xu <coxu@redhat.com>
---
 include/linux/kexec.h |  4 ++++
 kernel/kexec_file.c   | 21 +++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index f0e9f8eda7a3..c45bfc727737 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -171,6 +171,7 @@ int kexec_image_post_load_cleanup_default(struct kimage *image);
  * @buf_min:	The buffer can't be placed below this address.
  * @buf_max:	The buffer can't be placed above this address.
  * @top_down:	Allocate from top of memory.
+ * @random:	Place the buffer at a random position.
  */
 struct kexec_buf {
 	struct kimage *image;
@@ -182,6 +183,9 @@ struct kexec_buf {
 	unsigned long buf_min;
 	unsigned long buf_max;
 	bool top_down;
+#ifdef CONFIG_CRASH_DUMP
+	bool random;
+#endif
 };
 
 int kexec_load_purgatory(struct kimage *image, struct kexec_buf *kbuf);
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 3d64290d24c9..f7538d8f67e0 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -25,6 +25,9 @@
 #include <linux/elfcore.h>
 #include <linux/kernel.h>
 #include <linux/kernel_read_file.h>
+#ifdef CONFIG_CRASH_DUMP
+#include <linux/prandom.h>
+#endif
 #include <linux/syscalls.h>
 #include <linux/vmalloc.h>
 #include "kexec_internal.h"
@@ -437,6 +440,18 @@ SYSCALL_DEFINE5(kexec_file_load, int, kernel_fd, int, initrd_fd,
 	return ret;
 }
 
+#ifdef CONFIG_CRASH_DUMP
+static unsigned long kexec_random_start(unsigned long start, unsigned long end)
+{
+	unsigned long temp_start;
+	unsigned short i;
+
+	get_random_bytes(&i, sizeof(unsigned short));
+	temp_start = start + (end - start) / USHRT_MAX * i;
+	return temp_start;
+}
+#endif
+
 static int locate_mem_hole_top_down(unsigned long start, unsigned long end,
 				    struct kexec_buf *kbuf)
 {
@@ -445,6 +460,10 @@ static int locate_mem_hole_top_down(unsigned long start, unsigned long end,
 
 	temp_end = min(end, kbuf->buf_max);
 	temp_start = temp_end - kbuf->memsz + 1;
+#ifdef CONFIG_CRASH_DUMP
+	if (kbuf->random)
+		temp_start = kexec_random_start(temp_start, temp_end);
+#endif
 
 	do {
 		/* align down start */
@@ -482,6 +501,8 @@ static int locate_mem_hole_bottom_up(unsigned long start, unsigned long end,
 	unsigned long temp_start, temp_end;
 
 	temp_start = max(start, kbuf->buf_min);
+	if (kbuf->random)
+		temp_start = kexec_random_start(temp_start, end);
 
 	do {
 		temp_start = ALIGN(temp_start, kbuf->buf_align);
-- 
2.45.1
Re: [PATCH v5 1/7] kexec_file: allow to place kexec_buf randomly
Posted by Greg KH 1 year, 8 months ago 
On Fri, Jun 07, 2024 at 08:26:11PM +0800, Coiby Xu wrote:
> Currently, kexec_buf is placed in order which means for the same
> machine, the info in the kexec_buf is always located at the same
> position each time the machine is booted. This may cause a risk for
> sensitive information like LUKS volume key. Now struct kexec_buf has a
> new field random which indicates it's supposed to be placed in a random
> position.
> 
> Suggested-by: Jan Pazdziora <jpazdziora@redhat.com>
> Signed-off-by: Coiby Xu <coxu@redhat.com>
> ---
>  include/linux/kexec.h |  4 ++++
>  kernel/kexec_file.c   | 21 +++++++++++++++++++++
>  2 files changed, 25 insertions(+)
> 
> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> index f0e9f8eda7a3..c45bfc727737 100644
> --- a/include/linux/kexec.h
> +++ b/include/linux/kexec.h
> @@ -171,6 +171,7 @@ int kexec_image_post_load_cleanup_default(struct kimage *image);
>   * @buf_min:	The buffer can't be placed below this address.
>   * @buf_max:	The buffer can't be placed above this address.
>   * @top_down:	Allocate from top of memory.
> + * @random:	Place the buffer at a random position.
>   */
>  struct kexec_buf {
>  	struct kimage *image;
> @@ -182,6 +183,9 @@ struct kexec_buf {
>  	unsigned long buf_min;
>  	unsigned long buf_max;
>  	bool top_down;
> +#ifdef CONFIG_CRASH_DUMP
> +	bool random;
> +#endif

Why is the ifdef needed?

>  };
>  
>  int kexec_load_purgatory(struct kimage *image, struct kexec_buf *kbuf);
> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> index 3d64290d24c9..f7538d8f67e0 100644
> --- a/kernel/kexec_file.c
> +++ b/kernel/kexec_file.c
> @@ -25,6 +25,9 @@
>  #include <linux/elfcore.h>
>  #include <linux/kernel.h>
>  #include <linux/kernel_read_file.h>
> +#ifdef CONFIG_CRASH_DUMP
> +#include <linux/prandom.h>
> +#endif

No ifdef in .c files please.  This should not be an issue.

>  #include <linux/syscalls.h>
>  #include <linux/vmalloc.h>
>  #include "kexec_internal.h"
> @@ -437,6 +440,18 @@ SYSCALL_DEFINE5(kexec_file_load, int, kernel_fd, int, initrd_fd,
>  	return ret;
>  }
>  
> +#ifdef CONFIG_CRASH_DUMP
> +static unsigned long kexec_random_start(unsigned long start, unsigned long end)
> +{
> +	unsigned long temp_start;
> +	unsigned short i;
> +
> +	get_random_bytes(&i, sizeof(unsigned short));
> +	temp_start = start + (end - start) / USHRT_MAX * i;
> +	return temp_start;
> +}
> +#endif

This #ifdef should be handled properly in the .h file.

> +
>  static int locate_mem_hole_top_down(unsigned long start, unsigned long end,
>  				    struct kexec_buf *kbuf)
>  {
> @@ -445,6 +460,10 @@ static int locate_mem_hole_top_down(unsigned long start, unsigned long end,
>  
>  	temp_end = min(end, kbuf->buf_max);
>  	temp_start = temp_end - kbuf->memsz + 1;
> +#ifdef CONFIG_CRASH_DUMP
> +	if (kbuf->random)
> +		temp_start = kexec_random_start(temp_start, temp_end);
> +#endif

Same with this.

And why do you need the boolean at all, why not just have
kexec_random_start() handle this properly for you?

thanks,

greg k-h
Re: [PATCH v5 1/7] kexec_file: allow to place kexec_buf randomly
Posted by kernel test robot 1 year, 8 months ago 
Hi Coiby,

kernel test robot noticed the following build errors:

[auto build test ERROR on 8a92980606e3585d72d510a03b59906e96755b8a]

url:    https://github.com/intel-lab-lkp/linux/commits/Coiby-Xu/kexec_file-allow-to-place-kexec_buf-randomly/20240607-203154
base:   8a92980606e3585d72d510a03b59906e96755b8a
patch link:    https://lore.kernel.org/r/20240607122622.167228-2-coxu%40redhat.com
patch subject: [PATCH v5 1/7] kexec_file: allow to place kexec_buf randomly
config: x86_64-kexec (https://download.01.org/0day-ci/archive/20240608/202406081214.kNbwlJWP-lkp@intel.com/config)
compiler: clang version 18.1.5 (https://github.com/llvm/llvm-project 617a15a9eac96088ae5e9134248d8236e34b91b1)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240608/202406081214.kNbwlJWP-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202406081214.kNbwlJWP-lkp@intel.com/

All errors (new ones prefixed by >>):

>> kernel/kexec_file.c:504:12: error: no member named 'random' in 'struct kexec_buf'
     504 |         if (kbuf->random)
         |             ~~~~  ^
>> kernel/kexec_file.c:505:16: error: call to undeclared function 'kexec_random_start'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
     505 |                 temp_start = kexec_random_start(temp_start, end);
         |                              ^
   2 errors generated.


vim +504 kernel/kexec_file.c

   496	
   497	static int locate_mem_hole_bottom_up(unsigned long start, unsigned long end,
   498					     struct kexec_buf *kbuf)
   499	{
   500		struct kimage *image = kbuf->image;
   501		unsigned long temp_start, temp_end;
   502	
   503		temp_start = max(start, kbuf->buf_min);
 > 504		if (kbuf->random)
 > 505			temp_start = kexec_random_start(temp_start, end);
   506	
   507		do {
   508			temp_start = ALIGN(temp_start, kbuf->buf_align);
   509			temp_end = temp_start + kbuf->memsz - 1;
   510	
   511			if (temp_end > end || temp_end > kbuf->buf_max)
   512				return 0;
   513			/*
   514			 * Make sure this does not conflict with any of existing
   515			 * segments
   516			 */
   517			if (kimage_is_destination_range(image, temp_start, temp_end)) {
   518				temp_start = temp_start + PAGE_SIZE;
   519				continue;
   520			}
   521	
   522			/* We found a suitable memory range */
   523			break;
   524		} while (1);
   525	
   526		/* If we are here, we found a suitable memory range */
   527		kbuf->mem = temp_start;
   528	
   529		/* Success, stop navigating through remaining System RAM ranges */
   530		return 1;
   531	}
   532	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
Re: [PATCH v5 1/7] kexec_file: allow to place kexec_buf randomly
Posted by kernel test robot 1 year, 8 months ago 
Hi Coiby,

kernel test robot noticed the following build errors:

[auto build test ERROR on 8a92980606e3585d72d510a03b59906e96755b8a]

url:    https://github.com/intel-lab-lkp/linux/commits/Coiby-Xu/kexec_file-allow-to-place-kexec_buf-randomly/20240607-203154
base:   8a92980606e3585d72d510a03b59906e96755b8a
patch link:    https://lore.kernel.org/r/20240607122622.167228-2-coxu%40redhat.com
patch subject: [PATCH v5 1/7] kexec_file: allow to place kexec_buf randomly
config: parisc-allyesconfig (https://download.01.org/0day-ci/archive/20240608/202406081124.hYZYvBL0-lkp@intel.com/config)
compiler: hppa-linux-gcc (GCC) 13.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240608/202406081124.hYZYvBL0-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202406081124.hYZYvBL0-lkp@intel.com/

All errors (new ones prefixed by >>):

   kernel/kexec_file.c: In function 'locate_mem_hole_bottom_up':
>> kernel/kexec_file.c:504:17: error: 'struct kexec_buf' has no member named 'random'
     504 |         if (kbuf->random)
         |                 ^~
>> kernel/kexec_file.c:505:30: error: implicit declaration of function 'kexec_random_start' [-Werror=implicit-function-declaration]
     505 |                 temp_start = kexec_random_start(temp_start, end);
         |                              ^~~~~~~~~~~~~~~~~~
   cc1: some warnings being treated as errors


vim +504 kernel/kexec_file.c

   496	
   497	static int locate_mem_hole_bottom_up(unsigned long start, unsigned long end,
   498					     struct kexec_buf *kbuf)
   499	{
   500		struct kimage *image = kbuf->image;
   501		unsigned long temp_start, temp_end;
   502	
   503		temp_start = max(start, kbuf->buf_min);
 > 504		if (kbuf->random)
 > 505			temp_start = kexec_random_start(temp_start, end);
   506	
   507		do {
   508			temp_start = ALIGN(temp_start, kbuf->buf_align);
   509			temp_end = temp_start + kbuf->memsz - 1;
   510	
   511			if (temp_end > end || temp_end > kbuf->buf_max)
   512				return 0;
   513			/*
   514			 * Make sure this does not conflict with any of existing
   515			 * segments
   516			 */
   517			if (kimage_is_destination_range(image, temp_start, temp_end)) {
   518				temp_start = temp_start + PAGE_SIZE;
   519				continue;
   520			}
   521	
   522			/* We found a suitable memory range */
   523			break;
   524		} while (1);
   525	
   526		/* If we are here, we found a suitable memory range */
   527		kbuf->mem = temp_start;
   528	
   529		/* Success, stop navigating through remaining System RAM ranges */
   530		return 1;
   531	}
   532	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

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