Re: [PATCH v11 1/9] arm64: Add HAVE_REGS_AND_STACK_ACCESS_API feature

From: James Morse <james.morse@arm.com>
To: David Long <dave.long@linaro.org>
Cc: "Catalin Marinas" <catalin.marinas@arm.com>,
	"Will Deacon" <will.deacon@arm.com>,
	"Sandeepa Prabhu" <sandeepa.s.prabhu@gmail.com>,
	"William Cohen" <wcohen@redhat.com>,
	"Pratyush Anand" <panand@redhat.com>,
	"Steve Capper" <steve.capper@linaro.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org,
	"Marc Zyngier" <marc.zyngier@arm.com>,
	"Dave P Martin" <Dave.Martin@arm.com>,
	"Mark Rutland" <mark.rutland@arm.com>,
	"Robin Murphy" <Robin.Murphy@arm.com>,
	"Ard Biesheuvel" <ard.biesheuvel@linaro.org>,
	"Jens Wiklander" <jens.wiklander@linaro.org>,
	"Christoffer Dall" <christoffer.dall@linaro.org>,
	"Alex Bennée" <alex.bennee@linaro.org>,
	"Yang Shi" <yang.shi@linaro.org>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Viresh Kumar" <viresh.kumar@linaro.org>,
	"Suzuki K. Poulose" <suzuki.poulose@arm.com>,
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	"Zi Shen Lim" <zlim.lnx@gmail.com>,
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	"Balamurugan Shanmugam" <bshanmugam@apm.com>,
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	"Petr Mladek" <pmladek@suse.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Mark Brown" <broonie@kernel.org>
Subject: Re: [PATCH v11 1/9] arm64: Add HAVE_REGS_AND_STACK_ACCESS_API feature
Date: Fri, 11 Mar 2016 18:07:10 +0000	[thread overview]
Message-ID: <56E3094E.5010906@arm.com> (raw)
In-Reply-To: <1457501543-24197-2-git-send-email-dave.long@linaro.org>

Hi David,

On 09/03/16 05:32, David Long wrote:
> From: "David A. Long" <dave.long@linaro.org>
> 
> Add HAVE_REGS_AND_STACK_ACCESS_API feature for arm64.
> 
> Signed-off-by: David A. Long <dave.long@linaro.org>

> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
> index ff7f132..efebf0f 100644
> --- a/arch/arm64/kernel/ptrace.c
> +++ b/arch/arm64/kernel/ptrace.c

[ ... SNIP ... ]

> +/**
> + * regs_within_kernel_stack() - check the address in the stack
> + * @regs:      pt_regs which contains kernel stack pointer.
> + * @addr:      address which is checked.
> + *
> + * regs_within_kernel_stack() checks @addr is within the kernel stack page(s).
> + * If @addr is within the kernel stack, it returns true. If not, returns false.
> + */
> +bool regs_within_kernel_stack(struct pt_regs *regs, unsigned long addr)
> +{
> +	return ((addr & ~(THREAD_SIZE - 1))  ==
> +		(kernel_stack_pointer(regs) & ~(THREAD_SIZE - 1)));

I'm not sure where this is called from, but if kernel_stack_pointer(regs) could
ever point into an irq_stack you will get the wrong result.

arch/arm64/include/asm/irq.h has 'on_irq_stack(sp, cpu)' which should help,
although you will need to check the bounds of the irq_stack separately.

The horrible details...

>From arch/arm64/kernel/irq.c:20
> /* irq stack only needs to be 16 byte aligned - not IRQ_STACK_SIZE aligned. */
> DEFINE_PER_CPU(unsigned long [IRQ_STACK_SIZE/sizeof(long)], irq_stack)
> __aligned(16);

This was because per-cpu variables can be at-most page aligned.
6cdf9c7ca687 ("arm64: Store struct thread_info in sp_el0") changed
current_thread_info() to work on these weirdly aligned irq_stacks.

Thanks,

James