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Commit 8c9a134c authored by Kees Cook's avatar Kees Cook Committed by Linus Torvalds
Browse files

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: default avatarKees Cook <keescook@chromium.org>
Reviewed-by: default avatarAndrew 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent a670468f

Documentation/admin-guide/kernel-parameters.txt

+3 −2
Original line number Diff line number Diff line
@@ -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>

mm/Kconfig.debug

+3 −3
Original line number Diff line number Diff line
@@ -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"