On 12/20/23 12:15, Mimi Zohar wrote:
Hi Tushar,
The Subject line should include the word "extra". The use of the
extra memory isn't limited to the measurements between the kexec load
and exec. Additional records could be added as a result of the kexec
load itself. Let's simplify the title to "ima: make the kexec extra
memory configurable".
Please remove any references to measurements between kexec load and
execute.
Thanks Mimi. I will make these changes.
On Fri, 2023-12-15 at 17:07 -0800, Tushar Sugandhi wrote:
IMA currently allocates half a PAGE_SIZE for the extra events that would
be measured between kexec 'load' and 'execute'. Depending on the IMA
policy and the system state, that memory may not be sufficient to hold
the extra IMA events measured after kexec 'load'. The memory
requirements vary from system to system and they should be configurable.
The extra memory allocated for carrying the IMA measurement list across
kexec is hardcoded as a half a PAGE. Make it configurable.
Will do.
Define a Kconfig option, IMA_KEXEC_EXTRA_MEMORY_KB, to configure the
extra memory (in kb) to be allocated for IMA measurements added in the
window from kexec 'load' to kexec 'execute'.
Update ima_add_kexec_buffer() function to allocate memory based on the
Kconfig option value, rather than the currently hardcoded one.
Signed-off-by: Tushar Sugandhi <tusharsu@xxxxxxxxxxxxxxxxxxx>
---
security/integrity/ima/Kconfig | 9 +++++++++
security/integrity/ima/ima_kexec.c | 13 ++++++++-----
2 files changed, 17 insertions(+), 5 deletions(-)
diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
index 60a511c6b583..8792b7aab768 100644
--- a/security/integrity/ima/Kconfig
+++ b/security/integrity/ima/Kconfig
@@ -338,3 +338,12 @@ config IMA_DISABLE_HTABLE
default n
help
This option disables htable to allow measurement of duplicate records.
+
+config IMA_KEXEC_EXTRA_MEMORY_KB
+ int
+ depends on IMA && IMA_KEXEC
+ default 64
Since this isn't optional, the default should remain as a half page.
Since a page is architecture specific, the default will need to be arch
specific.
thanks,
Mimih
It was a feedback from Stefan in the V2 of this series to convert it
from number of PAGES to KB.[1]
But I can revert it to number of pages again.
Also, making the default value as a fraction (1/2 page) feels weird for
a CONFIG variable.
Is it ok to make the default value as one page rather than half page?
[1]
https://lore.kernel.org/all/15a12e79-2e90-28f7-ffa3-ff470c673099@xxxxxxxxxxxxx/
>>> +config IMA_KEXEC_EXTRA_PAGES
>>> + int
>>> + depends on IMA && IMA_KEXEC
>>> + default 16
>>> + help
>>> + IMA_KEXEC_EXTRA_PAGES determines the number of extra
>>> + pages to be allocated for IMA measurements added in the
>>> + window from kexec 'load' to kexec 'execute'.
>>
>>
>> On ppc64 a page is 64kb. I would ask for additional kb here.
>>
>>
> Not sure I understand. Do you mean I should make the default value of
> the config IMA_KEXEC_EXTRA_PAGES 64 or something?
No, what I mean is you should ask the user for how many extra kilobytes
(kb) to allocate - not ask for pages.
Stefan
+ help
+ IMA_KEXEC_EXTRA_MEMORY_KB determines the extra memory to be
+ allocated (in kb) for IMA measurements added in the window
+ from kexec 'load' to kexec 'execute'.
diff --git a/security/integrity/ima/ima_kexec.c b/security/integrity/ima/ima_kexec.c
index 55bd5362262e..063da9c834a0 100644
--- a/security/integrity/ima/ima_kexec.c
+++ b/security/integrity/ima/ima_kexec.c
@@ -128,15 +128,18 @@ void ima_add_kexec_buffer(struct kimage *image)
int ret;
/*
- * Reserve an extra half page of memory for additional measurements
- * added during the kexec load.
+ * Reserve extra memory for measurements added in the window from
+ * kexec 'load' to kexec 'execute'.
*/
- binary_runtime_size = ima_get_binary_runtime_size();
+ binary_runtime_size = ima_get_binary_runtime_size() +
+ sizeof(struct ima_kexec_hdr) +
+ (CONFIG_IMA_KEXEC_EXTRA_MEMORY_KB * 1024);
+
if (binary_runtime_size >= ULONG_MAX - PAGE_SIZE)
kexec_segment_size = ULONG_MAX;
else
- kexec_segment_size = ALIGN(ima_get_binary_runtime_size() +
- PAGE_SIZE / 2, PAGE_SIZE);
+ kexec_segment_size = ALIGN(binary_runtime_size, PAGE_SIZE);
+
if ((kexec_segment_size == ULONG_MAX) ||
((kexec_segment_size >> PAGE_SHIFT) > totalram_pages() / 2)) {
pr_err("Binary measurement list too large.\n");
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