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mm: clarify CONFIG_PAGE_POISONING and usage 

The Kconfig text for CONFIG_PAGE_POISONING doesn't mention that it has to
be enabled explicitly.  This updates the documentation for that and adds a
note about CONFIG_PAGE_POISONING to the "page_poison" command line docs.
While here, change description of CONFIG_PAGE_POISONING_ZERO too, as it's
not "random" data, but rather the fixed debugging value that would be used
when not zeroing.  Additionally removes a stray "bool" in the Kconfig.

Link: http://lkml.kernel.org/r/20180725223832.GA43733@beast
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Laura Abbott <labbott@redhat.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Kees Cook 2018-08-21 21:53:10 -07:00 committed by Linus Torvalds
parent a670468f5e
commit 8c9a134cae
2 changed files with 6 additions and 5 deletions
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5
Documentation/admin-guide/kernel-parameters.txt
View File

@ -3041,8 +3041,9 @@
on: enable the feature
page_poison= [KNL] Boot-time parameter changing the state of
poisoning on the buddy allocator.
off: turn off poisoning
poisoning on the buddy allocator, available with
CONFIG_PAGE_POISONING=y.
off: turn off poisoning (default)
on: turn on poisoning
panic= [KNL] Kernel behaviour on panic: delay <timeout>

6
mm/Kconfig.debug
View File

@ -46,7 +46,8 @@ config PAGE_POISONING
Fill the pages with poison patterns after free_pages() and verify
the patterns before alloc_pages. The filling of the memory helps
reduce the risk of information leaks from freed data. This does
have a potential performance impact.
have a potential performance impact if enabled with the
"page_poison=1" kernel boot option.
Note that "poison" here is not the same thing as the "HWPoison"
for CONFIG_MEMORY_FAILURE. This is software poisoning only.
@ -65,7 +66,7 @@ config PAGE_POISONING_NO_SANITY
say N.
config PAGE_POISONING_ZERO
bool "Use zero for poisoning instead of random data"
bool "Use zero for poisoning instead of debugging value"
depends on PAGE_POISONING
---help---
Instead of using the existing poison value, fill the pages with
@ -75,7 +76,6 @@ config PAGE_POISONING_ZERO
allocation.
If unsure, say N
bool
config DEBUG_PAGE_REF
bool "Enable tracepoint to track down page reference manipulation"