Re: [PATCH v5 04/15] arm64: errata: Add detection for TRBE write to out-of-range

Mathieu Poirier
2021-10-18T15:50:54Z

Good morning,

On Thu, Oct 14, 2021 at 11:31:14PM +0100, Suzuki K Poulose wrote:
> Arm Neoverse-N2 and Cortex-A710 cores are affected by an erratum where the
> trbe, under some circumstances, might write upto 64bytes to an address after

Checkpatch gives me a warning about this line...

> the Limit as programmed by the TRBLIMITR_EL1.LIMIT. This might -
>
> - Corrupt a page in the ring buffer, which may corrupt trace from a
> previous session, consumed by userspace.
> - Hit the guard page at the end of the vmalloc area and raise a fault.
>
> To keep the handling simpler, we always leave the last page from the
> range, which TRBE is allowed to write. This can be achieved by ensuring
> that we always have more than a PAGE worth space in the range, while
> calculating the LIMIT for TRBE. And then the LIMIT pointer can be adjusted
> to leave the PAGE (TRBLIMITR.LIMIT -= PAGE_SIZE), out of the TRBE range
> while enabling it. This makes sure that the TRBE will only write to an area
> within its allowed limit (i.e, [head-head+size]) and we do not have to handle

I'm pretty sure this line will also be flagged.

> address faults within the driver.
>
> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
> Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
> Cc: Mike Leach <mike.leach@linaro.org>
> Cc: Leo Yan <leo.yan@linaro.org>
> Cc: Will Deacon <will@kernel.org>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
> Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
> Acked-by: Catalin Marinas <catalin.marinas@arm.com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> ---
> Documentation/arm64/silicon-errata.rst | 4 +++
> arch/arm64/Kconfig | 41 ++++++++++++++++++++++++++
> arch/arm64/kernel/cpu_errata.c | 20 +++++++++++++
> arch/arm64/tools/cpucaps | 1 +
> 4 files changed, 66 insertions(+)
>
> diff --git a/Documentation/arm64/silicon-errata.rst b/Documentation/arm64/silicon-errata.rst
> index 569a92411dcd..5342e895fb60 100644
> --- a/Documentation/arm64/silicon-errata.rst
> +++ b/Documentation/arm64/silicon-errata.rst
> @@ -96,6 +96,8 @@ stable kernels.
> +----------------+-----------------+-----------------+-----------------------------+
> | ARM | Cortex-A710 | #2054223 | ARM64_ERRATUM_2054223 |
> +----------------+-----------------+-----------------+-----------------------------+
> +| ARM | Cortex-A710 | #2224489 | ARM64_ERRATUM_2224489 |
> ++----------------+-----------------+-----------------+-----------------------------+
> | ARM | Neoverse-N1 | #1188873,1418040| ARM64_ERRATUM_1418040 |
> +----------------+-----------------+-----------------+-----------------------------+
> | ARM | Neoverse-N1 | #1349291 | N/A |
> @@ -106,6 +108,8 @@ stable kernels.
> +----------------+-----------------+-----------------+-----------------------------+
> | ARM | Neoverse-N2 | #2067961 | ARM64_ERRATUM_2067961 |
> +----------------+-----------------+-----------------+-----------------------------+
> +| ARM | Neoverse-N2 | #2253138 | ARM64_ERRATUM_2253138 |
> ++----------------+-----------------+-----------------+-----------------------------+
> | ARM | MMU-500 | #841119,826419 | N/A |
> +----------------+-----------------+-----------------+-----------------------------+
> +----------------+-----------------+-----------------+-----------------------------+
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 39b78460b9d0..f30029f4a9f9 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -740,6 +740,47 @@ config ARM64_ERRATUM_2067961
>
> If unsure, say Y.
>
> +config ARM64_WORKAROUND_TRBE_WRITE_OUT_OF_RANGE
> + bool
> +
> +config ARM64_ERRATUM_2253138
> + bool "Neoverse-N2: 2253138: workaround TRBE writing to address out-of-range"
> + depends on COMPILE_TEST # Until the CoreSight TRBE driver changes are in
> + depends on CORESIGHT_TRBE
> + default y
> + select ARM64_WORKAROUND_TRBE_WRITE_OUT_OF_RANGE
> + help
> + This option adds the workaround for ARM Neoverse-N2 erratum 2253138.
> +
> + Affected Neoverse-N2 cores might write to an out-of-range address, not reserved
> + for TRBE. Under some conditions, the TRBE might generate a write to the next
> + virtually addressed page following the last page of the TRBE address space
> + (i.e., the TRBLIMITR_EL1.LIMIT), instead of wrapping around to the base.
> +
> + Work around this in the driver by always making sure that there is a
> + page beyond the TRBLIMITR_EL1.LIMIT, within the space allowed for the TRBE.
> +
> + If unsure, say Y.
> +
> +config ARM64_ERRATUM_2224489
> + bool "Cortex-A710: 2224489: workaround TRBE writing to address out-of-range"
> + depends on COMPILE_TEST # Until the CoreSight TRBE driver changes are in
> + depends on CORESIGHT_TRBE
> + default y
> + select ARM64_WORKAROUND_TRBE_WRITE_OUT_OF_RANGE
> + help
> + This option adds the workaround for ARM Cortex-A710 erratum 2224489.
> +
> + Affected Cortex-A710 cores might write to an out-of-range address, not reserved
> + for TRBE. Under some conditions, the TRBE might generate a write to the next
> + virtually addressed page following the last page of the TRBE address space
> + (i.e., the TRBLIMITR_EL1.LIMIT), instead of wrapping around to the base.
> +
> + Work around this in the driver by always making sure that there is a
> + page beyond the TRBLIMITR_EL1.LIMIT, within the space allowed for the TRBE.
> +
> + If unsure, say Y.
> +
> config CAVIUM_ERRATUM_22375
> bool "Cavium erratum 22375, 24313"
> default y
> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
> index bdbeac75ead6..e2978b89d4b8 100644
> --- a/arch/arm64/kernel/cpu_errata.c
> +++ b/arch/arm64/kernel/cpu_errata.c
> @@ -364,6 +364,18 @@ static const struct midr_range tsb_flush_fail_cpus[] = {
> };
> #endif /* CONFIG_ARM64_WORKAROUND_TSB_FLUSH_FAILURE */
>
> +#ifdef CONFIG_ARM64_WORKAROUND_TRBE_WRITE_OUT_OF_RANGE
> +static struct midr_range trbe_write_out_of_range_cpus[] = {
> +#ifdef CONFIG_ARM64_ERRATUM_2253138
> + MIDR_ALL_VERSIONS(MIDR_NEOVERSE_N2),
> +#endif
> +#ifdef CONFIG_ARM64_ERRATUM_2224489
> + MIDR_ALL_VERSIONS(MIDR_CORTEX_A710),
> +#endif
> + {},
> +};
> +#endif /* CONFIG_ARM64_WORKAROUND_TRBE_WRITE_OUT_OF_RANGE */
> +
> const struct arm64_cpu_capabilities arm64_errata[] = {
> #ifdef CONFIG_ARM64_WORKAROUND_CLEAN_CACHE
> {
> @@ -577,6 +589,14 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
> .capability = ARM64_WORKAROUND_TSB_FLUSH_FAILURE,
> ERRATA_MIDR_RANGE_LIST(tsb_flush_fail_cpus),
> },
> +#endif
> +#ifdef CONFIG_ARM64_WORKAROUND_TRBE_WRITE_OUT_OF_RANGE
> + {
> + .desc = "ARM erratum 2253138 or 2224489",
> + .capability = ARM64_WORKAROUND_TRBE_WRITE_OUT_OF_RANGE,
> + .type = ARM64_CPUCAP_WEAK_LOCAL_CPU_FEATURE,
> + CAP_MIDR_RANGE_LIST(trbe_write_out_of_range_cpus),
> + },
> #endif
> {
> }
> diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
> index 2102e15af43d..90628638e0f9 100644
> --- a/arch/arm64/tools/cpucaps
> +++ b/arch/arm64/tools/cpucaps
> @@ -55,6 +55,7 @@ WORKAROUND_1508412
> WORKAROUND_1542419
> WORKAROUND_TRBE_OVERWRITE_FILL_MODE
> WORKAROUND_TSB_FLUSH_FAILURE
> +WORKAROUND_TRBE_WRITE_OUT_OF_RANGE
> WORKAROUND_CAVIUM_23154
> WORKAROUND_CAVIUM_27456
> WORKAROUND_CAVIUM_30115
> --
> 2.25.4
>