kernel/linux.git/drivers/char/hw_random, 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

hwrng: ks-sa - fix division by zero in ks_sa_rng_init

2025-10-15T10:00:18+00:00

[ Upstream commit 612b1dfeb414dfa780a6316014ceddf9a74ff5c0 ] Fix division by zero in ks_sa_rng_init caused by missing clock pointer initialization. The clk_get_rate() call is performed on an uninitialized clk pointer, resulting in division by zero when calculating delay values. Add clock initialization code before using the clock. Fixes: 6d01d8511dce ("hwrng: ks-sa - Add minimum sleep time before ready-polling") Signed-off-by: Nishanth Menon drivers/char/hw_random/ks-sa-rng.c | 7 +++++++ 1 file changed, 7 insertions(+) Reviewed-by: Alexander Sverdlin Signed-off-by: Herbert Xu Signed-off-by: Sasha Levin

hwrng: nomadik - add ARM_AMBA dependency

2025-10-15T10:00:05+00:00

[ Upstream commit efaa2d815a0e4d1c06750e587100f6f7f4ee5497 ] Compile-testing this driver is only possible when the AMBA bus driver is available in the kernel: x86_64-linux-ld: drivers/char/hw_random/nomadik-rng.o: in function `nmk_rng_remove': nomadik-rng.c:(.text+0x67): undefined reference to `amba_release_regions' x86_64-linux-ld: drivers/char/hw_random/nomadik-rng.o: in function `nmk_rng_probe': nomadik-rng.c:(.text+0xee): undefined reference to `amba_request_regions' x86_64-linux-ld: nomadik-rng.c:(.text+0x18d): undefined reference to `amba_release_regions' The was previously implied by the 'depends on ARCH_NOMADIK', but needs to be specified for the COMPILE_TEST case. Fixes: d5e93b3374e4 ("hwrng: Kconfig - Add helper dependency on COMPILE_TEST") Signed-off-by: Arnd Bergmann Signed-off-by: Herbert Xu Signed-off-by: Sasha Levin

hwrng: mtk - handle devm_pm_runtime_enable errors

2025-08-15T10:13:55+00:00

[ Upstream commit 522a242a18adc5c63a24836715dbeec4dc3faee1 ] Although unlikely, devm_pm_runtime_enable() call might fail, so handle the return value. Fixes: 78cb66caa6ab ("hwrng: mtk - Use devm_pm_runtime_enable") Signed-off-by: Ovidiu Panait Signed-off-by: Herbert Xu Signed-off-by: Sasha Levin

hwrng: mtk - Use devm_pm_runtime_enable

2024-09-06T06:50:45+00:00

Replace pm_runtime_enable with the devres-enabled version which can trigger pm_runtime_disable. Otherwise, the below appears during reload driver. mtk_rng 1020f000.rng: Unbalanced pm_runtime_enable! Fixes: 81d2b34508c6 ("hwrng: mtk - add runtime PM support") Cc: Suggested-by: Chen-Yu Tsai Signed-off-by: Guoqing Jiang Signed-off-by: Herbert Xu

hwrng: rockchip - handle devm_pm_runtime_enable errors

2024-08-30T10:22:31+00:00

It's unlikely that devm_pm_runtime_enable ever fails. Still, it makes sense to read the return value and handle errors. Signed-off-by: Martin Kaiser Signed-off-by: Herbert Xu

hwrng: rockchip - rst is used only during probe

2024-08-30T10:22:31+00:00

The driver uses the rst variable only for an initial reset when the chip is probed. There's no need to store rst in the driver's private data, we can make it a local variable in the probe function. Signed-off-by: Martin Kaiser Signed-off-by: Herbert Xu

hwrng: mxc-rnga - Use devm_clk_get_enabled() helpers

2024-08-30T10:22:31+00:00

The devm_clk_get_enabled() helpers: - call devm_clk_get() - call clk_prepare_enable() and register what is needed in order to call clk_disable_unprepare() when needed, as a managed resource. This simplifies the code and avoids the calls to clk_disable_unprepare(). Signed-off-by: Huan Yang Reviewed-by: Martin Kaiser Signed-off-by: Herbert Xu

hwrng: cctrng - Add missing clk_disable_unprepare in cctrng_resume

2024-08-10T04:25:34+00:00

Add the missing clk_disable_unprepare() before return in cctrng_resume(). Fixes: a583ed310bb6 ("hwrng: cctrng - introduce Arm CryptoCell driver") Cc: Signed-off-by: Gaosheng Cui Signed-off-by: Herbert Xu