Re: [PATCH v7 4/6] arm64: cpufeature: Modify address authentication cpufeature to exact

From: Catalin Marinas <catalin.marinas@arm.com>
To: Amit Kachhap <amit.kachhap@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Mark Brown <broonie@kernel.org>,
	James Morse <james.morse@arm.com>,
	Vincenzo Frascino <Vincenzo.Frascino@arm.com>,
	Will Deacon <will@kernel.org>, Dave Martin <Dave.Martin@arm.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v7 4/6] arm64: cpufeature: Modify address authentication cpufeature to exact
Date: Mon, 14 Sep 2020 11:04:33 +0100	[thread overview]
Message-ID: <20200914100432.GA32700@gaia> (raw)
In-Reply-To: <8128f714-0f99-1113-de41-03d35b89c5b6@arm.com>

On Mon, Sep 14, 2020 at 12:24:23PM +0530, Amit Kachhap wrote:
> On 9/11/20 10:54 PM, Catalin Marinas wrote:
> > On Wed, Sep 09, 2020 at 07:37:57PM +0530, Amit Daniel Kachhap wrote:
> > > The current address authentication cpufeature levels are set as LOWER_SAFE
> > > which is not compatible with the different configurations added for Armv8.3
> > > ptrauth enhancements as the different levels have different behaviour and
> > > there is no tunable to enable the lower safe versions. This is rectified
> > > by setting those cpufeature type as EXACT.
> > > 
> > > The current cpufeature framework also does not interfere in the booting of
> > > non-exact secondary cpus but rather marks them as tainted. As a workaround
> > > this is fixed by replacing the generic match handler with a new handler
> > > specific to ptrauth.
> > > 
> > > After this change, if there is any variation in ptrauth configurations in
> > > secondary cpus from boot cpu then those mismatched cpus are parked in an
> > > infinite loop.
> > > 
> > > Following ptrauth crash log is oberserved in Arm fastmodel with mismatched
> > > cpus without this fix,
> > > 
> > >   CPU features: SANITY CHECK: Unexpected variation in SYS_ID_AA64ISAR1_EL1. Boot CPU: 0x11111110211402, CPU4: 0x11111110211102
> > >   CPU features: Unsupported CPU feature variation detected.
> > >   GICv3: CPU4: found redistributor 100 region 0:0x000000002f180000
> > >   CPU4: Booted secondary processor 0x0000000100 [0x410fd0f0]
> > >   Unable to handle kernel paging request at virtual address bfff800010dadf3c
> > >   Mem abort info:
> > >     ESR = 0x86000004
> > >     EC = 0x21: IABT (current EL), IL = 32 bits
> > >     SET = 0, FnV = 0
> > >     EA = 0, S1PTW = 0
> > >   [bfff800010dadf3c] address between user and kernel address ranges
> > >   Internal error: Oops: 86000004 [#1] PREEMPT SMP
> > >   Modules linked in:
> > >   CPU: 4 PID: 29 Comm: migration/4 Tainted: G S                5.8.0-rc4-00005-ge658591d66d1-dirty #158
> > >   Hardware name: Foundation-v8A (DT)
> > >   pstate: 60000089 (nZCv daIf -PAN -UAO BTYPE=--)
> > >   pc : 0xbfff800010dadf3c
> > >   lr : __schedule+0x2b4/0x5a8
> > >   sp : ffff800012043d70
> > >   x29: ffff800012043d70 x28: 0080000000000000
> > >   x27: ffff800011cbe000 x26: ffff00087ad37580
> > >   x25: ffff00087ad37000 x24: ffff800010de7d50
> > >   x23: ffff800011674018 x22: 0784800010dae2a8
> > >   x21: ffff00087ad37000 x20: ffff00087acb8000
> > >   x19: ffff00087f742100 x18: 0000000000000030
> > >   x17: 0000000000000000 x16: 0000000000000000
> > >   x15: ffff800011ac1000 x14: 00000000000001bd
> > >   x13: 0000000000000000 x12: 0000000000000000
> > >   x11: 0000000000000000 x10: 71519a147ddfeb82
> > >   x9 : 825d5ec0fb246314 x8 : ffff00087ad37dd8
> > >   x7 : 0000000000000000 x6 : 00000000fffedb0e
> > >   x5 : 00000000ffffffff x4 : 0000000000000000
> > >   x3 : 0000000000000028 x2 : ffff80086e11e000
> > >   x1 : ffff00087ad37000 x0 : ffff00087acdc600
> > >   Call trace:
> > >    0xbfff800010dadf3c
> > >    schedule+0x78/0x110
> > >    schedule_preempt_disabled+0x24/0x40
> > >    __kthread_parkme+0x68/0xd0
> > >    kthread+0x138/0x160
> > >    ret_from_fork+0x10/0x34
> > >   Code: bad PC value
> > 
> > That's what FTR_EXACT gives us. The variation above is in the field at
> > bit position 8 (API_SHIFT) with the boot CPU value of 4 and the
> > secondary CPU of 1, if I read it correctly.
> 
> Yes
> 
> > Would it be better if the incompatible CPUs are just parked? I'm trying
> > to figure out from the verify_local_cpu_caps() code whether that's
> > possible. I don't fully understand why we don't trigger the "Detected
> > conflict for capability" message instead.
> 
> The above ptrauth crash appears when this fix patch is not present and
> with this fix present, cpu4 is actually parked as,
> 
> [    0.098833] CPU features: CPU4: Detected conflict for capability 39
> (Address authentication (IMP DEF algorithm)), System: 1, CPU: 0
> [    0.098833] CPU4: will not boot

Ah, should have read the commit log properly. Thanks for the
clarification.

-- 
Catalin

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