riscv: hwprobe: Fix stale vDSO data for late-initialized keys at boot

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commit 5d15d2ad36 upstream.

The hwprobe vDSO data for some keys, like MISALIGNED_VECTOR_PERF,
is determined by an asynchronous kthread. This can create a race
condition where the kthread finishes after the vDSO data has
already been populated, causing userspace to read stale values.

To fix this race, a new 'ready' flag is added to the vDSO data,
initialized to 'false' during arch_initcall_sync. This flag is
checked by both the vDSO's user-space code and the riscv_hwprobe
syscall. The syscall serves as a one-time gate, using a completion
to wait for any pending probes before populating the data and
setting the flag to 'true', thus ensuring userspace reads fresh
values on its first request.

Reported-by: Tsukasa OI <research_trasio@irq.a4lg.com>
Closes: https://lore.kernel.org/linux-riscv/760d637b-b13b-4518-b6bf-883d55d44e7f@irq.a4lg.com/
Fixes: e7c9d66e31 ("RISC-V: Report vector unaligned access speed hwprobe")
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Alexandre Ghiti <alexghiti@rivosinc.com>
Cc: Olof Johansson <olof@lixom.net>
Cc: stable@vger.kernel.org
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Co-developed-by: Palmer Dabbelt <palmer@dabbelt.com>
Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>
Signed-off-by: Jingwei Wang <wangjingwei@iscas.ac.cn>
Link: https://lore.kernel.org/r/20250811142035.105820-1-wangjingwei@iscas.ac.cn
[pjw@kernel.org: fix checkpatch issues]
Signed-off-by: Paul Walmsley <pjw@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

...

This commit is contained in:

Jingwei Wang 2025-08-11 22:20:06 +08:00 • committed by Greg Kroah-Hartman

parent 3a01b2614e

commit 6dc769665a

5 changed files with 79 additions and 15 deletions

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7

arch/riscv/include/asm/hwprobe.h

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6

arch/riscv/include/asm/vdso/arch_data.h

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74

arch/riscv/kernel/sys_hwprobe.c

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9

arch/riscv/kernel/unaligned_access_speed.c

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2

arch/riscv/kernel/vdso/hwprobe.c

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