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[PATCH v4 5/5] arm64: add attrs and format to ptdump document

Maxwell Bland posted 5 patches 1 year, 6 months ago
There is a newer version of this series
[PATCH v4 5/5] arm64: add attrs and format to ptdump document
Posted by Maxwell Bland 1 year, 6 months ago 
Update the ptdump content with a precise explanation of the attribute
symbols and the identical-entry coalescing implicit in the code.

Remove unnecessary layout example given the existing cat example,
and opt instead for a precise, clear explantination of address markers,
format, attributes.

Update example to match the new cosmetic and intermediate-directory
printing changes.

Signed-off-by: Maxwell Bland <mbland@motorola.com>
---
 Documentation/arch/arm64/ptdump.rst | 126 ++++++++++++++--------------
 1 file changed, 61 insertions(+), 65 deletions(-)

diff --git a/Documentation/arch/arm64/ptdump.rst b/Documentation/arch/arm64/ptdump.rst
index 5dcfc5d7cddf..fee7600dd4d1 100644
--- a/Documentation/arch/arm64/ptdump.rst
+++ b/Documentation/arch/arm64/ptdump.rst
@@ -29,68 +29,64 @@ configurations and mount debugfs::
  mount -t debugfs nodev /sys/kernel/debug
  cat /sys/kernel/debug/kernel_page_tables
 
-On analysing the output of ``cat /sys/kernel/debug/kernel_page_tables``
-one can derive information about the virtual address range of the entry,
-followed by size of the memory region covered by this entry, the
-hierarchical structure of the page tables and finally the attributes
-associated with each page. The page attributes provide information about
-access permissions, execution capability, type of mapping such as leaf
-level PTE or block level PGD, PMD and PUD, and access status of a page
-within the kernel memory. Assessing these attributes can assist in
-understanding the memory layout, access patterns and security
-characteristics of the kernel pages.
-
-Kernel virtual memory layout example::
-
- start address        end address         size             attributes
- +---------------------------------------------------------------------------------------+
- | ---[ Linear Mapping start ]---------------------------------------------------------- |
- | ..................                                                                    |
- | 0xfff0000000000000-0xfff0000000210000  2112K PTE RW NX SHD AF  UXN  MEM/NORMAL-TAGGED |
- | 0xfff0000000210000-0xfff0000001c00000 26560K PTE ro NX SHD AF  UXN  MEM/NORMAL        |
- | ..................                                                                    |
- | ---[ Linear Mapping end ]------------------------------------------------------------ |
- +---------------------------------------------------------------------------------------+
- | ---[ Modules start ]----------------------------------------------------------------- |
- | ..................                                                                    |
- | 0xffff800000000000-0xffff800008000000   128M PTE                                      |
- | ..................                                                                    |
- | ---[ Modules end ]------------------------------------------------------------------- |
- +---------------------------------------------------------------------------------------+
- | ---[ vmalloc() area ]---------------------------------------------------------------- |
- | ..................                                                                    |
- | 0xffff800008010000-0xffff800008200000  1984K PTE ro x  SHD AF       UXN  MEM/NORMAL   |
- | 0xffff800008200000-0xffff800008e00000    12M PTE ro x  SHD AF  CON  UXN  MEM/NORMAL   |
- | ..................                                                                    |
- | ---[ vmalloc() end ]----------------------------------------------------------------- |
- +---------------------------------------------------------------------------------------+
- | ---[ Fixmap start ]------------------------------------------------------------------ |
- | ..................                                                                    |
- | 0xfffffbfffdb80000-0xfffffbfffdb90000    64K PTE ro x  SHD AF  UXN  MEM/NORMAL        |
- | 0xfffffbfffdb90000-0xfffffbfffdba0000    64K PTE ro NX SHD AF  UXN  MEM/NORMAL        |
- | ..................                                                                    |
- | ---[ Fixmap end ]-------------------------------------------------------------------- |
- +---------------------------------------------------------------------------------------+
- | ---[ PCI I/O start ]----------------------------------------------------------------- |
- | ..................                                                                    |
- | 0xfffffbfffe800000-0xfffffbffff800000    16M PTE                                      |
- | ..................                                                                    |
- | ---[ PCI I/O end ]------------------------------------------------------------------- |
- +---------------------------------------------------------------------------------------+
- | ---[ vmemmap start ]----------------------------------------------------------------- |
- | ..................                                                                    |
- | 0xfffffc0002000000-0xfffffc0002200000     2M PTE RW NX SHD AF  UXN  MEM/NORMAL        |
- | 0xfffffc0002200000-0xfffffc0020000000   478M PTE                                      |
- | ..................                                                                    |
- | ---[ vmemmap end ]------------------------------------------------------------------- |
- +---------------------------------------------------------------------------------------+
-
-``cat /sys/kernel/debug/kernel_page_tables`` output::
-
- 0xfff0000001c00000-0xfff0000080000000     2020M PTE  RW NX SHD AF   UXN    MEM/NORMAL-TAGGED
- 0xfff0000080000000-0xfff0000800000000       30G PMD
- 0xfff0000800000000-0xfff0000800700000        7M PTE  RW NX SHD AF   UXN    MEM/NORMAL-TAGGED
- 0xfff0000800700000-0xfff0000800710000       64K PTE  ro NX SHD AF   UXN    MEM/NORMAL-TAGGED
- 0xfff0000800710000-0xfff0000880000000  2089920K PTE  RW NX SHD AF   UXN    MEM/NORMAL-TAGGED
- 0xfff0000880000000-0xfff0040000000000     4062G PMD
- 0xfff0040000000000-0xffff800000000000     3964T PGD
+``/sys/kernel/debug/kernel_page_tables`` provides a line of information
+for each group of page table entries sharing the same attributes and
+type of mapping, i.e. leaf level PTE or block level PGD, PMD, and PUD.
+Assessing these attributes can assist in determining memory layout,
+access patterns and security characteristics of the kernel pages.
+
+Lines are formatted as follows::
+
+ <start_vaddr>-<end_vaddr> <size> <type> <attributes>
+
+Note that the set of attributes, and therefore formatting, is not
+equivalent between leaf and non-leaf entries. For example, PMD entries
+can support the PXNTable permission bit and do not share that same set
+of attributes as leaf level PTE entries.
+
+The following attributes are presently supported::
+
+F		Entry is invalid
+USER		Memory is user mapped
+ro		Memory is read-only
+RW		Memory is read-write
+NX		Memory is privileged execute never
+x               Memory is privileged executable
+SHD		Memory is shared
+AF		Entry accessed flag is set
+NG		Entry Not-Global flag is set
+CON		Entry contiguous bit is set
+UXN		Memory is unprivileged execute never
+GP		Memory supports BTI
+TBL		Entry is a table descriptor
+BLK		Entry is a block descriptor
+NXTbl		Entry's referenced table is PXN
+UXNTbl		Entry's referenced table is unprivileged execute never
+DEVICE/*	Entry is device memory, see ARM reference for types
+MEM/*		Entry is non-device memory, see ARM reference for types
+
+The beginning and end of each region is also delineated by a single line
+tag in the following format::
+
+ ---[ <marker_name> ]---
+
+With supported address markers including the kernel's linear mapping,
+kasan shadow memory, kernel modules memory, vmalloc memory, PCI I/O
+memory, and the kernel's fixmap region.
+
+Example ``cat /sys/kernel/debug/kernel_page_tables`` output::
+
+---[ Linear Mapping start ]---
+0xffff000000000000-0xffff31ffffffffff                  50T PGD
+0xffff320000000000-0xffffffffffffffff                 206T PGD   TBL     RW               x      NXTbl UXNTbl    MEM/NORMAL
+    0xffff320000000000-0xffff3251ffffffff             328G PUD
+    0xffff325200000000-0xffff32523fffffff               1G PUD   TBL     RW               x      NXTbl UXNTbl    MEM/NORMAL
+      0xffff325200000000-0xffff3252001fffff             2M PMD   TBL     RW               x      NXTbl UXNTbl    MEM/NORMAL
+        0xffff325200000000-0xffff3252001fffff           2M PTE       RW NX SHD AF NG     UXN    MEM/NORMAL-TAGGED
+      0xffff325200200000-0xffff3252003fffff             2M PMD   TBL     RW               x      NXTbl UXNTbl    MEM/NORMAL
+        0xffff325200200000-0xffff32520020ffff          64K PTE       RW NX SHD AF NG     UXN    MEM/NORMAL-TAGGED
+        0xffff325200210000-0xffff3252003fffff        1984K PTE       ro NX SHD AF NG     UXN    MEM/NORMAL
+      0xffff325200400000-0xffff325201dfffff            26M PMD   BLK     ro SHD AF NG     NX UXN                 MEM/NORMAL
+      0xffff325201e00000-0xffff325201ffffff             2M PMD   TBL     RW               x      NXTbl UXNTbl    MEM/NORMAL
+        0xffff325201e00000-0xffff325201e0ffff          64K PTE       ro NX SHD AF NG     UXN    MEM/NORMAL
+        0xffff325201e10000-0xffff325201ffffff        1984K PTE       RW NX SHD AF NG     UXN    MEM/NORMAL-TAGGED
-- 
2.39.2
Re: [PATCH v4 5/5] arm64: add attrs and format to ptdump document
Posted by Randy Dunlap 1 year, 6 months ago 
Hi,-

On 6/18/24 7:43 AM, Maxwell Bland wrote:
> Update the ptdump content with a precise explanation of the attribute
> symbols and the identical-entry coalescing implicit in the code.
> 
> Remove unnecessary layout example given the existing cat example,
> and opt instead for a precise, clear explantination of address markers,

                                       explanation

> format, attributes.
> 
> Update example to match the new cosmetic and intermediate-directory
> printing changes.
> 
> Signed-off-by: Maxwell Bland <mbland@motorola.com>
> ---
>  Documentation/arch/arm64/ptdump.rst | 126 ++++++++++++++--------------
>  1 file changed, 61 insertions(+), 65 deletions(-)
> 
> diff --git a/Documentation/arch/arm64/ptdump.rst b/Documentation/arch/arm64/ptdump.rst
> index 5dcfc5d7cddf..fee7600dd4d1 100644
> --- a/Documentation/arch/arm64/ptdump.rst
> +++ b/Documentation/arch/arm64/ptdump.rst
> @@ -29,68 +29,64 @@ configurations and mount debugfs::
>   mount -t debugfs nodev /sys/kernel/debug
>   cat /sys/kernel/debug/kernel_page_tables
>  
> -On analysing the output of ``cat /sys/kernel/debug/kernel_page_tables``
> -one can derive information about the virtual address range of the entry,
> -followed by size of the memory region covered by this entry, the
> -hierarchical structure of the page tables and finally the attributes
> -associated with each page. The page attributes provide information about
> -access permissions, execution capability, type of mapping such as leaf
> -level PTE or block level PGD, PMD and PUD, and access status of a page
> -within the kernel memory. Assessing these attributes can assist in
> -understanding the memory layout, access patterns and security
> -characteristics of the kernel pages.
> -
> -Kernel virtual memory layout example::
> -
> - start address        end address         size             attributes
> - +---------------------------------------------------------------------------------------+
> - | ---[ Linear Mapping start ]---------------------------------------------------------- |
> - | ..................                                                                    |
> - | 0xfff0000000000000-0xfff0000000210000  2112K PTE RW NX SHD AF  UXN  MEM/NORMAL-TAGGED |
> - | 0xfff0000000210000-0xfff0000001c00000 26560K PTE ro NX SHD AF  UXN  MEM/NORMAL        |
> - | ..................                                                                    |
> - | ---[ Linear Mapping end ]------------------------------------------------------------ |
> - +---------------------------------------------------------------------------------------+
> - | ---[ Modules start ]----------------------------------------------------------------- |
> - | ..................                                                                    |
> - | 0xffff800000000000-0xffff800008000000   128M PTE                                      |
> - | ..................                                                                    |
> - | ---[ Modules end ]------------------------------------------------------------------- |
> - +---------------------------------------------------------------------------------------+
> - | ---[ vmalloc() area ]---------------------------------------------------------------- |
> - | ..................                                                                    |
> - | 0xffff800008010000-0xffff800008200000  1984K PTE ro x  SHD AF       UXN  MEM/NORMAL   |
> - | 0xffff800008200000-0xffff800008e00000    12M PTE ro x  SHD AF  CON  UXN  MEM/NORMAL   |
> - | ..................                                                                    |
> - | ---[ vmalloc() end ]----------------------------------------------------------------- |
> - +---------------------------------------------------------------------------------------+
> - | ---[ Fixmap start ]------------------------------------------------------------------ |
> - | ..................                                                                    |
> - | 0xfffffbfffdb80000-0xfffffbfffdb90000    64K PTE ro x  SHD AF  UXN  MEM/NORMAL        |
> - | 0xfffffbfffdb90000-0xfffffbfffdba0000    64K PTE ro NX SHD AF  UXN  MEM/NORMAL        |
> - | ..................                                                                    |
> - | ---[ Fixmap end ]-------------------------------------------------------------------- |
> - +---------------------------------------------------------------------------------------+
> - | ---[ PCI I/O start ]----------------------------------------------------------------- |
> - | ..................                                                                    |
> - | 0xfffffbfffe800000-0xfffffbffff800000    16M PTE                                      |
> - | ..................                                                                    |
> - | ---[ PCI I/O end ]------------------------------------------------------------------- |
> - +---------------------------------------------------------------------------------------+
> - | ---[ vmemmap start ]----------------------------------------------------------------- |
> - | ..................                                                                    |
> - | 0xfffffc0002000000-0xfffffc0002200000     2M PTE RW NX SHD AF  UXN  MEM/NORMAL        |
> - | 0xfffffc0002200000-0xfffffc0020000000   478M PTE                                      |
> - | ..................                                                                    |
> - | ---[ vmemmap end ]------------------------------------------------------------------- |
> - +---------------------------------------------------------------------------------------+
> -
> -``cat /sys/kernel/debug/kernel_page_tables`` output::
> -
> - 0xfff0000001c00000-0xfff0000080000000     2020M PTE  RW NX SHD AF   UXN    MEM/NORMAL-TAGGED
> - 0xfff0000080000000-0xfff0000800000000       30G PMD
> - 0xfff0000800000000-0xfff0000800700000        7M PTE  RW NX SHD AF   UXN    MEM/NORMAL-TAGGED
> - 0xfff0000800700000-0xfff0000800710000       64K PTE  ro NX SHD AF   UXN    MEM/NORMAL-TAGGED
> - 0xfff0000800710000-0xfff0000880000000  2089920K PTE  RW NX SHD AF   UXN    MEM/NORMAL-TAGGED
> - 0xfff0000880000000-0xfff0040000000000     4062G PMD
> - 0xfff0040000000000-0xffff800000000000     3964T PGD
> +``/sys/kernel/debug/kernel_page_tables`` provides a line of information
> +for each group of page table entries sharing the same attributes and
> +type of mapping, i.e. leaf level PTE or block level PGD, PMD, and PUD.
> +Assessing these attributes can assist in determining memory layout,
> +access patterns and security characteristics of the kernel pages.
> +
> +Lines are formatted as follows::
> +
> + <start_vaddr>-<end_vaddr> <size> <type> <attributes>
> +
> +Note that the set of attributes, and therefore formatting, is not
> +equivalent between leaf and non-leaf entries. For example, PMD entries
> +can support the PXNTable permission bit and do not share that same set
> +of attributes as leaf level PTE entries.
> +
> +The following attributes are presently supported::
> +
> +F		Entry is invalid
> +USER		Memory is user mapped
> +ro		Memory is read-only
> +RW		Memory is read-write
> +NX		Memory is privileged execute never
> +x               Memory is privileged executable

Please use tabs above for indentation, like the other lines.

Why lower case x and ro but upper case for the others?

> +SHD		Memory is shared
> +AF		Entry accessed flag is set
> +NG		Entry Not-Global flag is set
> +CON		Entry contiguous bit is set
> +UXN		Memory is unprivileged execute never
> +GP		Memory supports BTI

Most of the abbreviations make some sense, but not that one (IMHO). ;)

> +TBL		Entry is a table descriptor
> +BLK		Entry is a block descriptor
> +NXTbl		Entry's referenced table is PXN
> +UXNTbl		Entry's referenced table is unprivileged execute never
> +DEVICE/*	Entry is device memory, see ARM reference for types
> +MEM/*		Entry is non-device memory, see ARM reference for types
> +
> +The beginning and end of each region is also delineated by a single line
> +tag in the following format::
> +
> + ---[ <marker_name> ]---
> +
> +With supported address markers including the kernel's linear mapping,
> +kasan shadow memory, kernel modules memory, vmalloc memory, PCI I/O
> +memory, and the kernel's fixmap region.
> +
> +Example ``cat /sys/kernel/debug/kernel_page_tables`` output::
> +
> +---[ Linear Mapping start ]---
> +0xffff000000000000-0xffff31ffffffffff                  50T PGD
> +0xffff320000000000-0xffffffffffffffff                 206T PGD   TBL     RW               x      NXTbl UXNTbl    MEM/NORMAL
> +    0xffff320000000000-0xffff3251ffffffff             328G PUD
> +    0xffff325200000000-0xffff32523fffffff               1G PUD   TBL     RW               x      NXTbl UXNTbl    MEM/NORMAL
> +      0xffff325200000000-0xffff3252001fffff             2M PMD   TBL     RW               x      NXTbl UXNTbl    MEM/NORMAL
> +        0xffff325200000000-0xffff3252001fffff           2M PTE       RW NX SHD AF NG     UXN    MEM/NORMAL-TAGGED
> +      0xffff325200200000-0xffff3252003fffff             2M PMD   TBL     RW               x      NXTbl UXNTbl    MEM/NORMAL
> +        0xffff325200200000-0xffff32520020ffff          64K PTE       RW NX SHD AF NG     UXN    MEM/NORMAL-TAGGED
> +        0xffff325200210000-0xffff3252003fffff        1984K PTE       ro NX SHD AF NG     UXN    MEM/NORMAL
> +      0xffff325200400000-0xffff325201dfffff            26M PMD   BLK     ro SHD AF NG     NX UXN                 MEM/NORMAL
> +      0xffff325201e00000-0xffff325201ffffff             2M PMD   TBL     RW               x      NXTbl UXNTbl    MEM/NORMAL
> +        0xffff325201e00000-0xffff325201e0ffff          64K PTE       ro NX SHD AF NG     UXN    MEM/NORMAL
> +        0xffff325201e10000-0xffff325201ffffff        1984K PTE       RW NX SHD AF NG     UXN    MEM/NORMAL-TAGGED

-- 
thanks.
~Randy
Re: [PATCH v4 5/5] arm64: add attrs and format to ptdump document
Posted by Maxwell Bland 1 year, 5 months ago 
On Tue, Jun 18, 2024 at 04:06:57PM GMT, Randy Dunlap wrote:
> On 6/18/24 7:43 AM, Maxwell Bland wrote:
> > +The following attributes are presently supported::
> > +
> > +F		Entry is invalid
> > +USER		Memory is user mapped
> > +ro		Memory is read-only
> > +RW		Memory is read-write
> > +NX		Memory is privileged execute never
> > +x               Memory is privileged executable
> 
> Why lower case x and ro but upper case for the others?
> 
> > +SHD		Memory is shared
> > +AF		Entry accessed flag is set
> > +NG		Entry Not-Global flag is set
> > +CON		Entry contiguous bit is set
> > +UXN		Memory is unprivileged execute never
> > +GP		Memory supports BTI
> 
> Most of the abbreviations make some sense, but not that one (IMHO). ;)

Hi Randy, thanks for the feedback above! I fixed these notes and
polished a few of the other acronyms as a result.

v5 is now here:
https://lore.kernel.org/all/2bcb3htsjhepxdybpw2bwot2jnuezl3p5mnj5rhjwgitlsufe7@xzhkyntridw3/

BRs,
Maxwell

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