linux-kernel - Re: [PATCH v4 05/40] iommu/io-pgtable-arm: Add quirk to quiet WARN

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250515143309.GA12165@willie-the-truck>
Date: Thu, 15 May 2025 15:33:10 +0100
From: Will Deacon <will@...nel.org>
To: Rob Clark <robdclark@...il.com>
Cc: dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
	linux-arm-msm@...r.kernel.org, Connor Abbott <cwabbott0@...il.com>,
	Rob Clark <robdclark@...omium.org>,
	Robin Murphy <robin.murphy@....com>, Joerg Roedel <joro@...tes.org>,
	Jason Gunthorpe <jgg@...pe.ca>, Nicolin Chen <nicolinc@...dia.com>,
	Kevin Tian <kevin.tian@...el.com>,
	Joao Martins <joao.m.martins@...cle.com>,
	"moderated list:ARM SMMU DRIVERS" <linux-arm-kernel@...ts.infradead.org>,
	"open list:IOMMU SUBSYSTEM" <iommu@...ts.linux.dev>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 05/40] iommu/io-pgtable-arm: Add quirk to quiet
 WARN_ON()

On Wed, May 14, 2025 at 10:53:19AM -0700, Rob Clark wrote:
> From: Rob Clark <robdclark@...omium.org>
> 
> In situations where mapping/unmapping sequence can be controlled by
> userspace, attempting to map over a region that has not yet been
> unmapped is an error.  But not something that should spam dmesg.
> 
> Now that there is a quirk, we can also drop the selftest_running
> flag, and use the quirk instead for selftests.
> 
> Signed-off-by: Rob Clark <robdclark@...omium.org>
> Acked-by: Robin Murphy <robin.murphy@....com>
> Signed-off-by: Rob Clark <robdclark@...omium.org>
> ---
>  drivers/iommu/io-pgtable-arm.c | 27 ++++++++++++++-------------
>  include/linux/io-pgtable.h     |  8 ++++++++
>  2 files changed, 22 insertions(+), 13 deletions(-)

[...]

> diff --git a/include/linux/io-pgtable.h b/include/linux/io-pgtable.h
> index bba2a51c87d2..639b8f4fb87d 100644
> --- a/include/linux/io-pgtable.h
> +++ b/include/linux/io-pgtable.h
> @@ -88,6 +88,13 @@ struct io_pgtable_cfg {
>  	 *
>  	 * IO_PGTABLE_QUIRK_ARM_HD: Enables dirty tracking in stage 1 pagetable.
>  	 * IO_PGTABLE_QUIRK_ARM_S2FWB: Use the FWB format for the MemAttrs bits
> +	 *
> +	 * IO_PGTABLE_QUIRK_NO_WARN_ON: Do not WARN_ON() on conflicting
> +	 *	mappings, but silently return -EEXISTS.  Normally an attempt
> +	 *	to map over an existing mapping would indicate some sort of
> +	 *	kernel bug, which would justify the WARN_ON().  But for GPU
> +	 *	drivers, this could be under control of userspace.  Which
> +	 *	deserves an error return, but not to spam dmesg.
>  	 */
>  	#define IO_PGTABLE_QUIRK_ARM_NS			BIT(0)
>  	#define IO_PGTABLE_QUIRK_NO_PERMS		BIT(1)
> @@ -97,6 +104,7 @@ struct io_pgtable_cfg {
>  	#define IO_PGTABLE_QUIRK_ARM_OUTER_WBWA		BIT(6)
>  	#define IO_PGTABLE_QUIRK_ARM_HD			BIT(7)
>  	#define IO_PGTABLE_QUIRK_ARM_S2FWB		BIT(8)
> +	#define IO_PGTABLE_QUIRK_NO_WARN_ON		BIT(9)

This feels a bit fragile to me:
  * IOMMU-API users of io-pgtable shouldn't be passing this quirk
    but might end up doing so to paper over driver bugs.

  * Low-level users of io-pgtable who expose page-table operations to
    userspace need to pass the quirk, but might well not bother because
    well-behaved userspace doesn't trigger the warning.

So overall, it's all a bit unsatisfactory. Is there a way we could have
the warnings only when invoked via the IOMMU API?

Will