From: Jason Gunthorpe <jgg@nvidia.com>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: David Hildenbrand <david@redhat.com>,
Catalin Marinas <catalin.marinas@arm.com>,
linux-mm@kvack.org, akpm@linux-foundation.org,
linuxppc-dev@lists.ozlabs.org
Subject: Re: get_user_pages() and EXEC_ONLY mapping.
Date: Fri, 10 Nov 2023 10:53:06 -0400 [thread overview]
Message-ID: <20231110145306.GP4488@nvidia.com> (raw)
In-Reply-To: <87bkc1oe8c.fsf@linux.ibm.com>
On Fri, Nov 10, 2023 at 08:19:23PM +0530, Aneesh Kumar K.V wrote:
>
> Hello,
>
> Some architectures can now support EXEC_ONLY mappings and I am wondering
> what get_user_pages() on those addresses should return.
-EPERM
> Earlier PROT_EXEC implied PROT_READ and pte_access_permitted()
> returned true for that. But arm64 does have this explicit comment
> that says
>
> /*
> * p??_access_permitted() is true for valid user mappings (PTE_USER
> * bit set, subject to the write permission check). For execute-only
> * mappings, like PROT_EXEC with EPAN (both PTE_USER and PTE_UXN bits
> * not set) must return false. PROT_NONE mappings do not have the
> * PTE_VALID bit set.
> */
>
> Is that correct? We should be able to get struct page for PROT_EXEC
> mappings?
If the memory is unreadable then providing a back door through
O_DIRECT and everthing else to read it sounds wrong to me.
If there is some case where a get_user_pages caller is exec-only
compatible then a new FOLL_EXEC flag to permit it would make sense.
Jason
WARNING: multiple messages have this Message-ID (diff)
From: Jason Gunthorpe <jgg@nvidia.com>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
David Hildenbrand <david@redhat.com>,
akpm@linux-foundation.org,
Christophe Leroy <christophe.leroy@csgroup.eu>,
linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: get_user_pages() and EXEC_ONLY mapping.
Date: Fri, 10 Nov 2023 10:53:06 -0400 [thread overview]
Message-ID: <20231110145306.GP4488@nvidia.com> (raw)
In-Reply-To: <87bkc1oe8c.fsf@linux.ibm.com>
On Fri, Nov 10, 2023 at 08:19:23PM +0530, Aneesh Kumar K.V wrote:
>
> Hello,
>
> Some architectures can now support EXEC_ONLY mappings and I am wondering
> what get_user_pages() on those addresses should return.
-EPERM
> Earlier PROT_EXEC implied PROT_READ and pte_access_permitted()
> returned true for that. But arm64 does have this explicit comment
> that says
>
> /*
> * p??_access_permitted() is true for valid user mappings (PTE_USER
> * bit set, subject to the write permission check). For execute-only
> * mappings, like PROT_EXEC with EPAN (both PTE_USER and PTE_UXN bits
> * not set) must return false. PROT_NONE mappings do not have the
> * PTE_VALID bit set.
> */
>
> Is that correct? We should be able to get struct page for PROT_EXEC
> mappings?
If the memory is unreadable then providing a back door through
O_DIRECT and everthing else to read it sounds wrong to me.
If there is some case where a get_user_pages caller is exec-only
compatible then a new FOLL_EXEC flag to permit it would make sense.
Jason
next prev parent reply other threads:[~2023-11-10 14:54 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-10 14:49 get_user_pages() and EXEC_ONLY mapping Aneesh Kumar K.V
2023-11-10 14:53 ` Jason Gunthorpe [this message]
2023-11-10 14:53 ` Jason Gunthorpe
2023-11-10 14:57 ` Aneesh Kumar K V
2023-11-10 15:06 ` Jason Gunthorpe
2023-11-10 15:06 ` Jason Gunthorpe
2023-11-10 17:17 ` Catalin Marinas
2023-11-10 17:17 ` Catalin Marinas
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