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Message-ID: <cf1deb9b-c5c4-4e85-891d-62ecf9a04e0f@lucifer.local>
Date: Mon, 28 Oct 2024 22:14:50 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
"Liam R. Howlett" <Liam.Howlett@...cle.com>,
Mark Brown <broonie@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Jann Horn <jannh@...gle.com>, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, Peter Xu <peterx@...hat.com>,
linux-arm-kernel@...ts.infradead.org,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>, Aishwarya TCV <Aishwarya.TCV@....com>
Subject: Re: [PATCH hotfix 6.12 v2 4/8] mm: resolve faulty mmap_region()
error path behaviour
On Mon, Oct 28, 2024 at 10:28:47PM +0100, Vlastimil Babka wrote:
> On 10/28/24 22:19, Linus Torvalds wrote:
> > On Mon, 28 Oct 2024 at 11:00, Vlastimil Babka <vbabka@...e.cz> wrote:
> >>
> >> VM_MTE_ALLOWED is also set by arm64's arch_calc_vm_flag_bits():
> >>
> >> if (system_supports_mte() && (flags & MAP_ANONYMOUS))
> >> return VM_MTE_ALLOWED;
> >
> > Yeah, but that should just move into arch_validate_flags() too.
> > There's no reason why that's done in a separate place.
> >
> > Linus
>
> Right, and VM_DATA_DEFAULT_FLAGS is only used in do_brk_flags() which is
> also an anonymous VMA, and it doesn't perform arch_validate_flags() anyway.
Unfortunately we can't do this and have everything work entirely
consistently.
This is because, while adding a file parameter to arch_validate_flags()
lets us do this shmem check, we can't be sure MAP_ANON was set and we do
not have access to this information at the point of the
arch_validate_flags() check.
We could check file == NULL, but this then excludes the MAP_ANON |
MAP_HUGETLB case which is (probably accidentally) permitted by
arch_calc_vm_flag_bits() and for the purposes of this fix we probably just
want to keep behaviour identical.
We could alternatively check the file is shmem _or_ hugetlb but this would
amount to a change in behaviour and not sure we want to go there.
Anyway I attach a patch that does what you suggest, I actually compiled
this one (!) but don't have a system set up to test it (Mark?)
If we bring this in it should probably be a separate commit...
----8<----
>From 247003cd2a4b5f4fc2dac97f5ef7e473a47f4324 Mon Sep 17 00:00:00 2001
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Date: Mon, 28 Oct 2024 22:05:44 +0000
Subject: [PATCH] mm: perform MTE check within arm64 hook entirely
It doesn't make sense to have shmem explicitly check this one arch-specific
case, it is arch-specific, so the arch should handle it. We know shmem is a
case in which we want to permit MTE, so simply check for this directly.
This also fixes the issue with checking arch_validate_flags() early, which
would otherwise break mmap_region().
In order to implement this we must pass a file pointer, and additionally
update the sparc code to accept this parameter too.
We'd ideally like to have eliminated the arch_calc_vm_flag_bits() case, but
we risk inadvertently changing behaviour as we do not have mmap() flags
available at the point of the arch_validate_flags() check and a MAP_ANON |
MAP_HUGETLB case would be accepted for MTE currently, but a MAP_SHARED |
MAP_HUGETLB would not.
This is likely an oversight but we want to try to keep behaviour identical
to before in this patch.
So continue to check VM_MTE_ALLOWED which arch_calc_vm_flag_bits() sets if
MAP_ANON.
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
---
arch/arm64/include/asm/mman.h | 18 ++++++++++++++----
arch/sparc/include/asm/mman.h | 5 +++--
include/linux/mman.h | 2 +-
mm/mmap.c | 4 ++--
mm/mprotect.c | 2 +-
mm/shmem.c | 3 ---
6 files changed, 21 insertions(+), 13 deletions(-)
diff --git a/arch/arm64/include/asm/mman.h b/arch/arm64/include/asm/mman.h
index 9e39217b4afb..44b7c8a1dd67 100644
--- a/arch/arm64/include/asm/mman.h
+++ b/arch/arm64/include/asm/mman.h
@@ -6,7 +6,9 @@
#ifndef BUILD_VDSO
#include <linux/compiler.h>
+#include <linux/fs.h>
#include <linux/types.h>
+#include <linux/shmem_fs.h>
static inline unsigned long arch_calc_vm_prot_bits(unsigned long prot,
unsigned long pkey)
@@ -60,15 +62,23 @@ static inline bool arch_validate_prot(unsigned long prot,
}
#define arch_validate_prot(prot, addr) arch_validate_prot(prot, addr)
-static inline bool arch_validate_flags(unsigned long vm_flags)
+static inline bool arch_validate_flags(struct file *file, unsigned long vm_flags)
{
if (!system_supports_mte())
return true;
- /* only allow VM_MTE if VM_MTE_ALLOWED has been set previously */
- return !(vm_flags & VM_MTE) || (vm_flags & VM_MTE_ALLOWED);
+ if (!(vm_flags & VM_MTE))
+ return true;
+
+ if (vm_flags & VM_MTE_ALLOWED)
+ return true;
+
+ if (shmem_file(file))
+ return true;
+
+ return false;
}
-#define arch_validate_flags(vm_flags) arch_validate_flags(vm_flags)
+#define arch_validate_flags(file, vm_flags) arch_validate_flags(file, vm_flags)
#endif /* !BUILD_VDSO */
diff --git a/arch/sparc/include/asm/mman.h b/arch/sparc/include/asm/mman.h
index af9c10c83dc5..d426e1f7c2c1 100644
--- a/arch/sparc/include/asm/mman.h
+++ b/arch/sparc/include/asm/mman.h
@@ -10,6 +10,7 @@ int sparc_mmap_check(unsigned long addr, unsigned long len);
#ifdef CONFIG_SPARC64
#include <asm/adi_64.h>
+#include <linux/fs.h>
static inline void ipi_set_tstate_mcde(void *arg)
{
@@ -54,11 +55,11 @@ static inline int sparc_validate_prot(unsigned long prot, unsigned long addr)
return 1;
}
-#define arch_validate_flags(vm_flags) arch_validate_flags(vm_flags)
+#define arch_validate_flags(file, vm_flags) arch_validate_flags(file, vm_flags)
/* arch_validate_flags() - Ensure combination of flags is valid for a
* VMA.
*/
-static inline bool arch_validate_flags(unsigned long vm_flags)
+static inline bool arch_validate_flags(struct file *file, unsigned long vm_flags)
{
/* If ADI is being enabled on this VMA, check for ADI
* capability on the platform and ensure VMA is suitable
diff --git a/include/linux/mman.h b/include/linux/mman.h
index 8ddca62d6460..82e6488026b7 100644
--- a/include/linux/mman.h
+++ b/include/linux/mman.h
@@ -117,7 +117,7 @@ static inline bool arch_validate_prot(unsigned long prot, unsigned long addr)
*
* Returns true if the VM_* flags are valid.
*/
-static inline bool arch_validate_flags(unsigned long flags)
+static inline bool arch_validate_flags(struct file *file, unsigned long flags)
{
return true;
}
diff --git a/mm/mmap.c b/mm/mmap.c
index 8462de1ee583..e06171d243ef 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1504,7 +1504,7 @@ static unsigned long __mmap_region(struct file *file, unsigned long addr,
#ifdef CONFIG_SPARC64
/* TODO: Fix SPARC ADI! */
- WARN_ON_ONCE(!arch_validate_flags(vm_flags));
+ WARN_ON_ONCE(!arch_validate_flags(file, vm_flags));
#endif
/* Lock the VMA since it is modified after insertion into VMA tree */
@@ -1587,7 +1587,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
return -EACCES;
/* Allow architectures to sanity-check the vm_flags. */
- if (!arch_validate_flags(vm_flags))
+ if (!arch_validate_flags(file, vm_flags))
return -EINVAL;
/* Map writable and ensure this isn't a sealed memfd. */
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 6f450af3252e..c6db98b893fc 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -816,7 +816,7 @@ static int do_mprotect_pkey(unsigned long start, size_t len,
}
/* Allow architectures to sanity-check the new flags */
- if (!arch_validate_flags(newflags)) {
+ if (!arch_validate_flags(vma->vm_file, newflags)) {
error = -EINVAL;
break;
}
diff --git a/mm/shmem.c b/mm/shmem.c
index 4ba1d00fabda..e87f5d6799a7 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2733,9 +2733,6 @@ static int shmem_mmap(struct file *file, struct vm_area_struct *vma)
if (ret)
return ret;
- /* arm64 - allow memory tagging on RAM-based files */
- vm_flags_set(vma, VM_MTE_ALLOWED);
-
file_accessed(file);
/* This is anonymous shared memory if it is unlinked at the time of mmap */
if (inode->i_nlink)
--
2.47.0
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