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linux/fs/pstore/Kconfig
Ard Biesheuvel 438b805003 pstore: Replace crypto API compression with zlib_deflate library calls 
Pstore supports compression using a variety of algorithms exposed by the
crypto API. This uses the deprecated comp (as opposed to scomp/acomp)
API, and so we should stop using that, and either move to the new API,
or switch to a different approach entirely.

Given that we only compress ASCII text in pstore, and considering that
this happens when the system is likely to be in an unstable state, the
flexibility that the complex crypto API provides does not outweigh its
impact on the risk that we might encounter additional problems when
trying to commit the kernel log contents to the pstore backend.

So let's switch [back] to the zlib deflate library API, and remove all
the complexity that really has no place in a low-level diagnostic
facility. Note that, while more modern compression algorithms have been
added to the kernel in recent years, the code size of zlib deflate is
substantially smaller than, e.g., zstd, while its performance in terms
of compression ratio is comparable for ASCII text, and speed is deemed
irrelevant in this context.

Note that this means that compressed pstore records may no longer be
accessible after a kernel upgrade, but this has never been part of the
contract. (The choice of compression algorithm is not stored in the
pstore records either)

Tested-by: "Guilherme G. Piccoli" <gpiccoli@igalia.com> # Steam Deck
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20230712162332.2670437-3-ardb@kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
2023-07-17 16:08:58 -07:00

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# SPDX-License-Identifier: GPL-2.0-only
config PSTORE
tristate "Persistent store support"
default n
help
This option enables generic access to platform level
persistent storage via "pstore" filesystem that can
be mounted as /dev/pstore. Only useful if you have
a platform level driver that registers with pstore to
provide the data, so you probably should just go say "Y"
(or "M") to a platform specific persistent store driver
(e.g. ACPI_APEI on X86) which will select this for you.
If you don't have a platform persistent store driver,
say N.
config PSTORE_DEFAULT_KMSG_BYTES
int "Default kernel log storage space" if EXPERT
depends on PSTORE
default "10240"
help
Defines default size of pstore kernel log storage.
Can be enlarged if needed, not recommended to shrink it.
config PSTORE_COMPRESS
bool "Pstore compression (deflate)"
depends on PSTORE
select ZLIB_INFLATE
select ZLIB_DEFLATE
default y
help
Whether pstore records should be compressed before being written to
the backing store. This is implemented using the zlib 'deflate'
algorithm, using the library implementation instead of using the full
blown crypto API. This reduces the risk of secondary oopses or other
problems while pstore is recording panic metadata.
config PSTORE_CONSOLE
bool "Log kernel console messages"
depends on PSTORE
help
When the option is enabled, pstore will log all kernel
messages, even if no oops or panic happened.
config PSTORE_PMSG
bool "Log user space messages"
depends on PSTORE
select RT_MUTEXES
help
When the option is enabled, pstore will export a character
interface /dev/pmsg0 to log user space messages. On reboot
data can be retrieved from /sys/fs/pstore/pmsg-ramoops-[ID].
If unsure, say N.
config PSTORE_FTRACE
bool "Persistent function tracer"
depends on PSTORE
depends on FUNCTION_TRACER
depends on DEBUG_FS
help
With this option kernel traces function calls into a persistent
ram buffer that can be decoded and dumped after reboot through
pstore filesystem. It can be used to determine what function
was last called before a reset or panic.
If unsure, say N.
config PSTORE_RAM
tristate "Log panic/oops to a RAM buffer"
depends on PSTORE
depends on HAS_IOMEM
select REED_SOLOMON
select REED_SOLOMON_ENC8
select REED_SOLOMON_DEC8
help
This enables panic and oops messages to be logged to a circular
buffer in RAM where it can be read back at some later point.
Note that for historical reasons, the module will be named
"ramoops.ko".
For more information, see Documentation/admin-guide/ramoops.rst.
config PSTORE_ZONE
tristate
depends on PSTORE
help
The common layer for pstore/blk (and pstore/ram in the future)
to manage storage in zones.
config PSTORE_BLK
tristate "Log panic/oops to a block device"
depends on PSTORE
depends on BLOCK
select PSTORE_ZONE
default n
help
This enables panic and oops message to be logged to a block dev
where it can be read back at some later point.
For more information, see Documentation/admin-guide/pstore-blk.rst
If unsure, say N.
config PSTORE_BLK_BLKDEV
string "block device identifier"
depends on PSTORE_BLK
default ""
help
Which block device should be used for pstore/blk.
It accepts the following variants:
1) <hex_major><hex_minor> device number in hexadecimal representation,
with no leading 0x, for example b302.
2) /dev/<disk_name> represents the device name of disk
3) /dev/<disk_name><decimal> represents the device name and number
of partition - device number of disk plus the partition number
4) /dev/<disk_name>p<decimal> - same as the above, this form is
used when disk name of partitioned disk ends with a digit.
5) PARTUUID=00112233-4455-6677-8899-AABBCCDDEEFF representing the
unique id of a partition if the partition table provides it.
The UUID may be either an EFI/GPT UUID, or refer to an MSDOS
partition using the format SSSSSSSS-PP, where SSSSSSSS is a zero-
filled hex representation of the 32-bit "NT disk signature", and PP
is a zero-filled hex representation of the 1-based partition number.
6) PARTUUID=<UUID>/PARTNROFF=<int> to select a partition in relation
to a partition with a known unique id.
7) <major>:<minor> major and minor number of the device separated by
a colon.
NOTE that, both Kconfig and module parameters can configure
pstore/blk, but module parameters have priority over Kconfig.
config PSTORE_BLK_KMSG_SIZE
int "Size in Kbytes of kmsg dump log to store"
depends on PSTORE_BLK
default 64
help
This just sets size of kmsg dump (oops, panic, etc) log for
pstore/blk. The size is in KB and must be a multiple of 4.
NOTE that, both Kconfig and module parameters can configure
pstore/blk, but module parameters have priority over Kconfig.
config PSTORE_BLK_MAX_REASON
int "Maximum kmsg dump reason to store"
depends on PSTORE_BLK
default 2
help
The maximum reason for kmsg dumps to store. The default is
2 (KMSG_DUMP_OOPS), see include/linux/kmsg_dump.h's
enum kmsg_dump_reason for more details.
NOTE that, both Kconfig and module parameters can configure
pstore/blk, but module parameters have priority over Kconfig.
config PSTORE_BLK_PMSG_SIZE
int "Size in Kbytes of pmsg to store"
depends on PSTORE_BLK
depends on PSTORE_PMSG
default 64
help
This just sets size of pmsg (pmsg_size) for pstore/blk. The size is
in KB and must be a multiple of 4.
NOTE that, both Kconfig and module parameters can configure
pstore/blk, but module parameters have priority over Kconfig.
config PSTORE_BLK_CONSOLE_SIZE
int "Size in Kbytes of console log to store"
depends on PSTORE_BLK
depends on PSTORE_CONSOLE
default 64
help
This just sets size of console log (console_size) to store via
pstore/blk. The size is in KB and must be a multiple of 4.
NOTE that, both Kconfig and module parameters can configure
pstore/blk, but module parameters have priority over Kconfig.
config PSTORE_BLK_FTRACE_SIZE
int "Size in Kbytes of ftrace log to store"
depends on PSTORE_BLK
depends on PSTORE_FTRACE
default 64
help
This just sets size of ftrace log (ftrace_size) for pstore/blk. The
size is in KB and must be a multiple of 4.
NOTE that, both Kconfig and module parameters can configure
pstore/blk, but module parameters have priority over Kconfig.
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