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Jonathan McDowell 24761c8441 hwrng: core - Allow runtime disabling of the HW RNG 
[ Upstream commit e74b96d77d ]

The HW RNG core allows for manual selection of which RNG device to use,
but does not allow for no device to be enabled. It may be desirable to
do this on systems with only a single suitable hardware RNG, where we
need exclusive access to other functionality on this device. In
particular when performing TPM firmware upgrades this lets us ensure the
kernel does not try to access the device.

Before:

root@debian-qemu-efi:~# grep "" /sys/devices/virtual/misc/hw_random/rng_*
/sys/devices/virtual/misc/hw_random/rng_available:tpm-rng-0
/sys/devices/virtual/misc/hw_random/rng_current:tpm-rng-0
/sys/devices/virtual/misc/hw_random/rng_quality:1024
/sys/devices/virtual/misc/hw_random/rng_selected:0

After:

root@debian-qemu-efi:~# grep "" /sys/devices/virtual/misc/hw_random/rng_*
/sys/devices/virtual/misc/hw_random/rng_available:tpm-rng-0 none
/sys/devices/virtual/misc/hw_random/rng_current:tpm-rng-0
/sys/devices/virtual/misc/hw_random/rng_quality:1024
/sys/devices/virtual/misc/hw_random/rng_selected:0

root@debian-qemu-efi:~# echo none > /sys/devices/virtual/misc/hw_random/rng_current
root@debian-qemu-efi:~# grep "" /sys/devices/virtual/misc/hw_random/rng_*
/sys/devices/virtual/misc/hw_random/rng_available:tpm-rng-0 none
/sys/devices/virtual/misc/hw_random/rng_current:none
grep: /sys/devices/virtual/misc/hw_random/rng_quality: No such device
/sys/devices/virtual/misc/hw_random/rng_selected:1

(Observe using bpftrace no calls to TPM being made)

root@debian-qemu-efi:~# echo "" > /sys/devices/virtual/misc/hw_random/rng_current
root@debian-qemu-efi:~# grep "" /sys/devices/virtual/misc/hw_random/rng_*
/sys/devices/virtual/misc/hw_random/rng_available:tpm-rng-0 none
/sys/devices/virtual/misc/hw_random/rng_current:tpm-rng-0
/sys/devices/virtual/misc/hw_random/rng_quality:1024
/sys/devices/virtual/misc/hw_random/rng_selected:0

(Observe using bpftrace that calls to the TPM resume)

Signed-off-by: Jonathan McDowell <noodles@meta.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Stable-dep-of: cc2f39d6ac ("hwrng: core - use RCU and work_struct to fix race condition")
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2026-03-04 07:19:40 -05:00
arch x86/fgraph,bpf: Switch kprobe_multi program stack unwind to hw_regs path 2026-03-04 07:19:37 -05:00
block block: add a bio_add_virt_nofail helper 2026-03-04 07:19:26 -05:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: authencesn - reject too-short AAD (assoclen<8) to match ESP/ESN spec 2026-01-30 10:28:39 +01:00
Documentation gpiolib-acpi: Update file references in the Documentation and MAINTAINERS 2026-02-11 13:40:29 +01:00
drivers hwrng: core - Allow runtime disabling of the HW RNG 2026-03-04 07:19:40 -05:00
fs fs/tests: exec: drop duplicate bprm_stack_limits test vectors 2026-03-04 07:19:40 -05:00
include mfd: wm8350-core: Use IRQF_ONESHOT 2026-03-04 07:19:39 -05:00
init init: handle bootloader identifier in kernel parameters 2025-10-19 16:33:50 +02:00
io_uring io_uring/sync: validate passed in offset 2026-03-04 07:19:28 -05:00
ipc ipc: fix to protect IPCS lookups using RCU 2025-06-27 11:11:22 +01:00
kernel sched/rt: Skip currently executing CPU in rto_next_cpu() 2026-03-04 07:19:40 -05:00
lib procfs: avoid fetching build ID while holding VMA lock 2026-02-11 13:40:18 +01:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm mm/hugetlb: fix excessive IPI broadcasts when unsharing PMD tables using mmu_gather 2026-02-19 16:29:55 +01:00
net bpf: Fix bpf_xdp_store_bytes proto for read-only arg 2026-03-04 07:19:38 -05:00
rust rust: rbtree: fix documentation typo in CursorMut peek_next method 2026-02-06 16:55:44 +01:00
samples samples/ftrace: Adjust LoongArch register restore order in direct calls 2026-01-08 10:14:50 +01:00
scripts scripts: generate_rust_analyzer: Add compiler_builtins -> core dep 2026-02-06 16:55:47 +01:00
security keys/trusted_keys: fix handle passed to tpm_buf_append_name during unseal 2026-01-30 10:28:44 +01:00
sound ASoC: fsl_xcvr: fix missing lock in fsl_xcvr_mode_put() 2026-02-19 16:29:54 +01:00
tools selftests/bpf: Fix resource leak in serial_test_wq on attach failure 2026-03-04 07:19:34 -05:00
usr kbuild: uapi: Strip comments before size type check 2025-11-13 15:34:35 -05:00
virt KVM: Don't clobber irqfd routing type when deassigning irqfd 2026-02-11 13:40:17 +01:00
.clang-format clang-format: Update with v6.11-rc1's for_each macro list 2024-08-02 13:20:31 +02:00
.clippy.toml rust: give Clippy the minimum supported Rust version 2025-08-01 09:48:44 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore rust: introduce .clippy.toml 2025-03-13 13:01:42 +01:00
.mailmap mailmap: add entry for Thorsten Blum 2024-11-07 14:14:59 -08:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Remove self from DSA entry 2024-11-03 12:52:38 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS gpiolib-acpi: Update file references in the Documentation and MAINTAINERS 2026-02-11 13:40:29 +01:00
Makefile Linux 6.12.74 2026-02-19 16:29:56 +01:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.