linux-kernel - Re: [PATCH] x86/pkeys: Disable PKU when XFEATURE

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Message-ID: <CAG8fp8RgxFz2pwv3BXJ=dMWxoLSKjBL8PN0N8kWqkDOCB2_ivg@mail.gmail.com>
Date: Thu, 20 Mar 2025 23:21:40 +0900
From: Akihiro Suda <suda.kyoto@...il.com>
To: Ingo Molnar <mingo@...nel.org>
Cc: Akihiro Suda <suda.gitsendemail@...il.com>, linux-kernel@...r.kernel.org, 
	x86@...nel.org, stable@...r.kernel.org, regressions@...ts.linux.dev, 
	aruna.ramakrishna@...cle.com, tglx@...utronix.de, 
	Akihiro Suda <akihiro.suda.cz@....ntt.co.jp>
Subject: Re: [PATCH] x86/pkeys: Disable PKU when XFEATURE_PKRU is missing

Thanks Ingo, but we may have to reconsider whether cpu_has_xfeatures
works in this place
https://lore.kernel.org/all/1b8745e0-ae80-4add-b015-affdaa69b369@intel.com/

The current code might be accidentally disabling PKU on other
PKU-compatible environments?

2025年3月20日(木) 6:39 Ingo Molnar <mingo@...nel.org>:
>
>
> * Akihiro Suda <suda.gitsendemail@...il.com> wrote:
>
> > Even when X86_FEATURE_PKU and X86_FEATURE_OSPKE are available,
> > XFEATURE_PKRU can be missing.
> > In such a case, pkeys has to be disabled to avoid hanging up.
> >
> >   WARNING: CPU: 0 PID: 1 at arch/x86/kernel/fpu/xstate.c:1003 get_xsave_addr_user+0x28/0x40
> >   (...)
> >   Call Trace:
> >    <TASK>
> >    ? get_xsave_addr_user+0x28/0x40
> >    ? __warn.cold+0x8e/0xea
> >    ? get_xsave_addr_user+0x28/0x40
> >    ? report_bug+0xff/0x140
> >    ? handle_bug+0x3b/0x70
> >    ? exc_invalid_op+0x17/0x70
> >    ? asm_exc_invalid_op+0x1a/0x20
> >    ? get_xsave_addr_user+0x28/0x40
> >    copy_fpstate_to_sigframe+0x1be/0x380
> >    ? __put_user_8+0x11/0x20
> >    get_sigframe+0xf1/0x280
> >    x64_setup_rt_frame+0x67/0x2c0
> >    arch_do_signal_or_restart+0x1b3/0x240
> >    syscall_exit_to_user_mode+0xb0/0x130
> >    do_syscall_64+0xab/0x1a0
> >    entry_SYSCALL_64_after_hwframe+0x77/0x7f
> >
> > This fix is known to be needed on Apple Virtualization.
> > Tested with macOS 13.5.2 running on MacBook Pro 2020 with
> > Intel(R) Core(TM) i7-1068NG7 CPU @ 2.30GHz.
> >
> > Fixes: 70044df250d0 ("x86/pkeys: Update PKRU to enable all pkeys before XSAVE")
> > Link: https://lore.kernel.org/regressions/CAG8fp8QvH71Wi_y7b7tgFp7knK38rfrF7rRHh-gFKqeS0gxY6Q@mail.gmail.com/T/#u
> > Link: https://github.com/lima-vm/lima/issues/3334
> >
> > Signed-off-by: Akihiro Suda <akihiro.suda.cz@....ntt.co.jp>
> > ---
> >  arch/x86/kernel/cpu/common.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> > index e9464fe411ac..4c2c268af214 100644
> > --- a/arch/x86/kernel/cpu/common.c
> > +++ b/arch/x86/kernel/cpu/common.c
> > @@ -517,7 +517,8 @@ static bool pku_disabled;
> >  static __always_inline void setup_pku(struct cpuinfo_x86 *c)
> >  {
> >       if (c == &boot_cpu_data) {
> > -             if (pku_disabled || !cpu_feature_enabled(X86_FEATURE_PKU))
> > +             if (pku_disabled || !cpu_feature_enabled(X86_FEATURE_PKU) ||
> > +                 !cpu_has_xfeatures(XFEATURE_PKRU, NULL))
> >                       return;
>
> Note that silent quirks are counterproductive, as they don't give VM
> vendors any incentives to fix their VM for such bugs.
>
> So I changed your quirk to be:
>
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -519,6 +519,17 @@ static __always_inline void setup_pku(struct cpuinfo_x86 *c)
>         if (c == &boot_cpu_data) {
>                 if (pku_disabled || !cpu_feature_enabled(X86_FEATURE_PKU))
>                         return;
> +               if (!cpu_has_xfeatures(XFEATURE_PKRU, NULL)) {
> +                       /*
> +                        * Missing XFEATURE_PKRU is not really a valid CPU
> +                        * configuration at this point, but apparently
> +                        * Apple Virtualization is affected by this,
> +                        * so return with a FW warning instead of crashing
> +                        * the bootup:
> +                        */
> +                       WARN_ONCE(1, FW_BUG "Invalid XFEATURE_PKRU configuration.\n");
> +                       return;
> +               }
>                 /*
>                  * Setting CR4.PKE will cause the X86_FEATURE_OSPKE cpuid
>                  * bit to be set.  Enforce it.
>
> This is noisy in the syslog, but it's a WARN_ONCE() and it doesn't
> crash the bootup.
>
> Thanks,
>
>         Ingo