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SubjectRe: [Patch v3 Part2 1/9] x86/microcode: Taint kernel only if microcode loading was successful
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On 2023/1/31 5:39, Ashok Raj wrote:
> Currently when late loading is aborted due to check_online_cpu(), kernel
> still ends up tainting the kernel.
>
> Taint only when microcode loading was successful.
>
> Suggested-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Ashok Raj <ashok.raj@intel.com>
> Cc: LKML <linux-kernel@vger.kernel.org>
> Cc: x86 <x86@kernel.org>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Tony Luck <tony.luck@intel.com>
> Cc: Dave Hansen <dave.hansen@intel.com>
> Cc: Alison Schofield <alison.schofield@intel.com>
> Cc: Reinette Chatre <reinette.chatre@intel.com>
> Cc: Thomas Gleixner (Intel) <tglx@linutronix.de>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: Stefan Talpalaru <stefantalpalaru@yahoo.com>
> Cc: David Woodhouse <dwmw2@infradead.org>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: Rafael J. Wysocki <rafael@kernel.org>
> Cc: Peter Zilstra (Intel) <peterz@infradead.org>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Andrew Cooper <Andrew.Cooper3@citrix.com>
> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> Cc: Martin Pohlack <mpohlack@amazon.de>
> ---
> v1->v2: (Thomas)
> - Remove unnecessary assignment of ret that's being overwritten.
> - Taint kernel only of loading was successful
> ---
> arch/x86/kernel/cpu/microcode/core.c | 19 +++++++++++++------
> 1 file changed, 13 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c
> index 61d57d9b93ee..1c6831b8b244 100644
> --- a/arch/x86/kernel/cpu/microcode/core.c
> +++ b/arch/x86/kernel/cpu/microcode/core.c
> @@ -472,7 +472,8 @@ static ssize_t reload_store(struct device *dev,
> enum ucode_state tmp_ret = UCODE_OK;
> int bsp = boot_cpu_data.cpu_index;
> unsigned long val;
> - ssize_t ret = 0;
> + int load_ret = -1;
> + ssize_t ret;
>
> ret = kstrtoul(buf, 0, &val);
> if (ret)
> @@ -488,20 +489,26 @@ static ssize_t reload_store(struct device *dev,
> goto put;
>
> tmp_ret = microcode_ops->request_microcode_fw(bsp, &microcode_pdev->dev);
> - if (tmp_ret != UCODE_NEW)
> + if (tmp_ret != UCODE_NEW) {
> + ret = size;
> goto put;
> + }
>
> mutex_lock(&microcode_mutex);
> - ret = microcode_reload_late();
> + load_ret = microcode_reload_late();
> mutex_unlock(&microcode_mutex);
>
> put:
> cpus_read_unlock();
>
> - if (ret == 0)
> + /*
> + * Taint only when loading was successful
> + */
> + if (load_ret == 0) {
> ret = size;

What about if loading was not successful(load_ret != 0)?
ret has no chance to be returned as size here and we'll run into the
endless update?

Thanks,
-Aubrey

> -
> - add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
> + add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
> + pr_warn("Microcode late loading tainted the kernel\n");
> + }
>
> return ret;
> }

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