kernel/linux.git/drivers/char/hw_random/core.c, branch v6.12.80

hwrng: core - use RCU and work_struct to fix race condition

2026-03-04T12:19:40+00:00

[ Upstream commit cc2f39d6ac48e6e3cb2d6240bc0d6df839dd0828 ] Currently, hwrng_fill is not cleared until the hwrng_fillfn() thread exits. Since hwrng_unregister() reads hwrng_fill outside the rng_mutex lock, a concurrent hwrng_unregister() may call kthread_stop() again on the same task. Additionally, if hwrng_unregister() is called immediately after hwrng_register(), the stopped thread may have never been executed. Thus, hwrng_fill remains dirty even after hwrng_unregister() returns. In this case, subsequent calls to hwrng_register() will fail to start new threads, and hwrng_unregister() will call kthread_stop() on the same freed task. In both cases, a use-after-free occurs: refcount_t: addition on 0; use-after-free. WARNING: ... at lib/refcount.c:25 refcount_warn_saturate+0xec/0x1c0 Call Trace: kthread_stop+0x181/0x360 hwrng_unregister+0x288/0x380 virtrng_remove+0xe3/0x200 This patch fixes the race by protecting the global hwrng_fill pointer inside the rng_mutex lock, so that hwrng_fillfn() thread is stopped only once, and calls to kthread_run() and kthread_stop() are serialized with the lock held. To avoid deadlock in hwrng_fillfn() while being stopped with the lock held, we convert current_rng to RCU, so that get_current_rng() can read current_rng without holding the lock. To remove the lock from put_rng(), we also delay the actual cleanup into a work_struct. Since get_current_rng() no longer returns ERR_PTR values, the IS_ERR() checks are removed from its callers. With hwrng_fill protected by the rng_mutex lock, hwrng_fillfn() can no longer clear hwrng_fill itself. Therefore, if hwrng_fillfn() returns directly after current_rng is dropped, kthread_stop() would be called on a freed task_struct later. To fix this, hwrng_fillfn() calls schedule() now to keep the task alive until being stopped. The kthread_stop() call is also moved from hwrng_unregister() to drop_current_rng(), ensuring kthread_stop() is called on all possible paths where current_rng becomes NULL, so that the thread would not wait forever. Fixes: be4000bc4644 ("hwrng: create filler thread") Suggested-by: Herbert Xu Signed-off-by: Lianjie Wang Signed-off-by: Herbert Xu Signed-off-by: Sasha Levin

hwrng: core - Allow runtime disabling of the HW RNG

2026-03-04T12:19:40+00:00

[ Upstream commit e74b96d77da9eb5ee1b603c937c2adab5134a04b ] 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 Signed-off-by: Herbert Xu Stable-dep-of: cc2f39d6ac48 ("hwrng: core - use RCU and work_struct to fix race condition") Signed-off-by: Sasha Levin

Merge tag 'v6.11-p1' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6

2024-07-19T15:52:58+00:00

Pull crypto update from Herbert Xu: "API: - Test setkey in no-SIMD context - Add skcipher speed test for user-specified algorithm Algorithms: - Add x25519 support on ppc64le - Add VAES and AVX512 / AVX10 optimized AES-GCM on x86 - Remove sm2 algorithm Drivers: - Add Allwinner H616 support to sun8i-ce - Use DMA in stm32 - Add Exynos850 hwrng support to exynos" * tag 'v6.11-p1' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6: (81 commits) hwrng: core - remove (un)register_miscdev() crypto: lib/mpi - delete unnecessary condition crypto: testmgr - generate power-of-2 lengths more often crypto: mxs-dcp - Ensure payload is zero when using key slot hwrng: Kconfig - Do not enable by default CN10K driver crypto: starfive - Fix nent assignment in rsa dec crypto: starfive - Align rsa input data to 32-bit crypto: qat - fix unintentional re-enabling of error interrupts crypto: qat - extend scope of lock in adf_cfg_add_key_value_param() Documentation: qat: fix auto_reset attribute details crypto: sun8i-ce - add Allwinner H616 support crypto: sun8i-ce - wrap accesses to descriptor address fields dt-bindings: crypto: sun8i-ce: Add compatible for H616 hwrng: core - Fix wrong quality calculation at hw rng registration hwrng: exynos - Enable Exynos850 support hwrng: exynos - Add SMC based TRNG operation hwrng: exynos - Implement bus clock control hwrng: exynos - Use devm_clk_get_enabled() to get the clock hwrng: exynos - Improve coding style dt-bindings: rng: Add Exynos850 support to exynos-trng ...

hwrng: core - remove (un)register_miscdev()

2024-07-12T23:50:28+00:00

These functions are redundant after commit 0daa7a0afd0f ("hwrng: Avoid manual device_create_file() calls"). Let's call misc_(de)register() directly. Signed-off-by: Masahiro Yamada Signed-off-by: Herbert Xu

hwrng: core - Fix wrong quality calculation at hw rng registration

2024-06-28T01:35:49+00:00

When there are rng sources registering at the hwrng core via hwrng_register() a struct hwrng is delivered. There is a quality field in there which is used to decide which of the registered hw rng sources will be used by the hwrng core. With commit 16bdbae39428 ("hwrng: core - treat default_quality as a maximum and default to 1024") there came in a new default of 1024 in case this field is empty and all the known hw rng sources at that time had been reworked to not fill this field and thus use the default of 1024. The code choosing the 'better' hw rng source during registration of a new hw rng source has never been adapted to this and thus used 0 if the hw rng implementation does not fill the quality field. So when two rng sources register, one with 0 (meaning 1024) and the other one with 999, the 999 hw rng will be chosen. As the later invoked function hwrng_init() anyway adjusts the quality field of the hw rng source, this adjustment is now done during registration of this new hw rng source. Tested on s390 with two hardware rng sources: crypto cards and trng true random generator device driver. Fixes: 16bdbae39428 ("hwrng: core - treat default_quality as a maximum and default to 1024") Reported-by: Christian Rund Suggested-by: Herbert Xu Signed-off-by: Harald Freudenberger Signed-off-by: Herbert Xu

hwrng: core - Remove add_early_randomness

2024-05-26T10:32:16+00:00

A potential deadlock was reported with the config file at https://web.archive.org/web/20240522052129/https://0x0.st/XPN_.txt In this particular configuration, the deadlock doesn't exist because the warning triggered at a point before modules were even available. However, the deadlock can be real because any module loaded would invoke async_synchronize_full. The issue is spurious for software crypto algorithms which aren't themselves involved in async probing. However, it would be hard to avoid for a PCI crypto driver using async probing. In this particular call trace, the problem is easily avoided because the only reason the module is being requested during probing is the add_early_randomness call in the hwrng core. This feature is vestigial since there is now a kernel thread dedicated to doing exactly this. So remove add_early_randomness as it is no longer needed. Reported-by: Nícolas F. R. A. Prado Reported-by: Eric Biggers Fixes: 1b6d7f9eb150 ("tpm: add session encryption protection to tpm2_get_random()") Link: https://lore.kernel.org/r/119dc5ed-f159-41be-9dda-1a056f29888d@notapiano/ Signed-off-by: Herbert Xu Reviewed-by: Jarkko Sakkinen Tested-by: Nícolas F. R. A. Prado Signed-off-by: Herbert Xu

hwrng: core - Convert sprintf/snprintf to sysfs_emit

2024-04-02T02:49:38+00:00

Per filesystems/sysfs.rst, show() should only use sysfs_emit() or sysfs_emit_at() when formatting the value to be returned to user space. coccinelle complains that there are still a couple of functions that use snprintf(). Convert them to sysfs_emit(). sprintf() will be converted as weel if they have. Generally, this patch is generated by make coccicheck M= MODE=patch \ COCCI=scripts/coccinelle/api/device_attr_show.cocci No functional change intended CC: Olivia Mackall CC: Herbert Xu CC: linux-crypto@vger.kernel.org Signed-off-by: Li Zhijian Signed-off-by: Herbert Xu

hwrng: core - Fix page fault dead lock on mmap-ed hwrng

2023-12-08T03:59:45+00:00

There is a dead-lock in the hwrng device read path. This triggers when the user reads from /dev/hwrng into memory also mmap-ed from /dev/hwrng. The resulting page fault triggers a recursive read which then dead-locks. Fix this by using a stack buffer when calling copy_to_user. Reported-by: Edward Adam Davis Reported-by: syzbot+c52ab18308964d248092@syzkaller.appspotmail.com Fixes: 9996508b3353 ("hwrng: core - Replace u32 in driver API with byte array") Cc: Signed-off-by: Herbert Xu

hwrng: bcm2835 - Fix hwrng throughput regression

2023-09-15T10:29:45+00:00

The last RCU stall fix caused a massive throughput regression of the hwrng on Raspberry Pi 0 - 3. hwrng_msleep doesn't sleep precisely enough and usleep_range doesn't allow scheduling. So try to restore the best possible throughput by introducing hwrng_yield which interruptable sleeps for one jiffy. Some performance measurements on Raspberry Pi 3B+ (arm64/defconfig): sudo dd if=/dev/hwrng of=/dev/null count=1 bs=10000 cpu_relax ~138025 Bytes / sec hwrng_msleep(1000) ~13 Bytes / sec hwrng_yield ~2510 Bytes / sec Fixes: 96cb9d055445 ("hwrng: bcm2835 - use hwrng_msleep() instead of cpu_relax()") Link: https://lore.kernel.org/linux-arm-kernel/bc97ece5-44a3-4c4e-77da-2db3eb66b128@gmx.net/ Signed-off-by: Stefan Wahren Reviewed-by: Jason A. Donenfeld Signed-off-by: Herbert Xu

hwrng: core - Remove duplicated include

2023-08-18T09:01:09+00:00

Remove duplicated include of linux/random.h. Resolves checkincludes message. And adjust includes in alphabetical order. Signed-off-by: GUO Zihua Signed-off-by: Herbert Xu