On Tue, Oct 29, 2024 at 04:36:32PM +0000, Lorenzo Stoakes wrote:
> On Tue, Oct 29, 2024 at 04:22:42PM +0000, Catalin Marinas wrote:
> > On Tue, Oct 29, 2024 at 03:16:00PM +0000, Lorenzo Stoakes wrote:
> > > On Tue, Oct 29, 2024 at 03:04:41PM +0000, Catalin Marinas wrote:
> > > > On Mon, Oct 28, 2024 at 10:14:50PM +0000, Lorenzo Stoakes wrote:
> > > > > So continue to check VM_MTE_ALLOWED which arch_calc_vm_flag_bits() sets if
> > > > > MAP_ANON.
> > > > [...]
> > > > > 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);
> > > >
> > > > This breaks arm64 KVM if the VMM uses shared mappings for the memory
> > > > slots (which is possible). We have kvm_vma_mte_allowed() that checks for
> > > > the VM_MTE_ALLOWED flag as the VMM may not use PROT_MTE/VM_MTE directly.
> > >
> > > Ugh yup missed that thanks.
> > >
> > > > I need to read this thread properly but why not pass the file argument
> > > > to arch_calc_vm_flag_bits() and set VM_MTE_ALLOWED in there?
> > >
> > > Can't really do that as it is entangled in a bunch of other stuff,
> > > e.g. calc_vm_prot_bits() would have to pass file and that's used in a bunch
> > > of places including arch code and... etc. etc.
> >
> > Not calc_vm_prot_bits() but calc_vm_flag_bits().
> > arch_calc_vm_flag_bits() is only implemented by two architectures -
> > arm64 and parisc and calc_vm_flag_bits() is only called from do_mmap().
> >
> > Basically we want to set VM_MTE_ALLOWED early during the mmap() call
> > and, at the time, my thinking was to do it in calc_vm_flag_bits(). The
> > calc_vm_prot_bits() OTOH is also called on the mprotect() path and is
> > responsible for translating PROT_MTE into a VM_MTE flag without any
> > checks. arch_validate_flags() would check if VM_MTE comes together with
> > VM_MTE_ALLOWED. But, as in the KVM case, that's not the only function
> > checking VM_MTE_ALLOWED.
> >
> > Since calc_vm_flag_bits() did not take a file argument, the lazy
> > approach was to add the flag explicitly for shmem (and hugetlbfs in
> > -next). But I think it would be easier to just add the file argument to
> > calc_vm_flag_bits() and do the check in the arch code to return
> > VM_MTE_ALLOWED. AFAICT, this is called before mmap_region() and
> > arch_validate_flags() (unless I missed something in the recent
> > reworking).
>
> I mean I totally get why you're suggesting it
Not sure ;)
> - it's the right _place_ but...
> It would require changes to a ton of code which is no good for a backport
> and we don't _need_ to do it.
>
> I'd rather do the smallest delta at this point, as I am not a huge fan of
> sticking it in here (I mean your point is wholly valid - it's at a better
> place to do so and we can change flags here, it's just - it's not where you
> expect to do this obviously).
>
> I mean for instance in arch/x86/kernel/cpu/sgx/encl.c (a file I'd _really_
> like us not to touch here by the way) we'd have to what pass NULL?
That's calc_vm_prot_bits(). I suggested calc_vm_flag_bits() (I know,
confusing names and total lack of inspiration when we added MTE
support). The latter is only called in one place - do_mmap().
That's what I meant (untested, on top of -next as it has a MAP_HUGETLB
check in there). I don't think it's much worse than your proposal,
assuming that it works:
diff --git a/arch/arm64/include/asm/mman.h b/arch/arm64/include/asm/mman.h
index 1dbfb56cb313..358bbaaafd41 100644
--- a/arch/arm64/include/asm/mman.h
+++ b/arch/arm64/include/asm/mman.h
@@ -6,6 +6,8 @@
#ifndef BUILD_VDSO
#include <linux/compiler.h>
+#include <linux/fs.h>
+#include <linux/shmem_fs.h>
#include <linux/types.h>
static inline unsigned long arch_calc_vm_prot_bits(unsigned long prot,
@@ -31,7 +33,7 @@ static inline unsigned long arch_calc_vm_prot_bits(unsigned long prot,
}
#define arch_calc_vm_prot_bits(prot, pkey) arch_calc_vm_prot_bits(prot, pkey)
-static inline unsigned long arch_calc_vm_flag_bits(unsigned long flags)
+static inline unsigned long arch_calc_vm_flag_bits(struct file *file, unsigned long flags)
{
/*
* Only allow MTE on anonymous mappings as these are guaranteed to be
@@ -39,12 +41,12 @@ static inline unsigned long arch_calc_vm_flag_bits(unsigned long flags)
* filesystem supporting MTE (RAM-based).
*/
if (system_supports_mte() &&
- (flags & (MAP_ANONYMOUS | MAP_HUGETLB)))
+ (flags & (MAP_ANONYMOUS | MAP_HUGETLB) || shmem_file(file)))
return VM_MTE_ALLOWED;
return 0;
}
-#define arch_calc_vm_flag_bits(flags) arch_calc_vm_flag_bits(flags)
+#define arch_calc_vm_flag_bits(file, flags) arch_calc_vm_flag_bits(file, flags)
static inline bool arch_validate_prot(unsigned long prot,
unsigned long addr __always_unused)
diff --git a/arch/parisc/include/asm/mman.h b/arch/parisc/include/asm/mman.h
index 89b6beeda0b8..663f587dc789 100644
--- a/arch/parisc/include/asm/mman.h
+++ b/arch/parisc/include/asm/mman.h
@@ -2,6 +2,7 @@
#ifndef __ASM_MMAN_H__
#define __ASM_MMAN_H__
+#include <linux/fs.h>
#include <uapi/asm/mman.h>
/* PARISC cannot allow mdwe as it needs writable stacks */
@@ -11,7 +12,7 @@ static inline bool arch_memory_deny_write_exec_supported(void)
}
#define arch_memory_deny_write_exec_supported arch_memory_deny_write_exec_supported
-static inline unsigned long arch_calc_vm_flag_bits(unsigned long flags)
+static inline unsigned long arch_calc_vm_flag_bits(struct file *file, unsigned long flags)
{
/*
* The stack on parisc grows upwards, so if userspace requests memory
@@ -23,6 +24,6 @@ static inline unsigned long arch_calc_vm_flag_bits(unsigned long flags)
return 0;
}
-#define arch_calc_vm_flag_bits(flags) arch_calc_vm_flag_bits(flags)
+#define arch_calc_vm_flag_bits(file, flags) arch_calc_vm_flag_bits(file, flags)
#endif /* __ASM_MMAN_H__ */
diff --git a/include/linux/mman.h b/include/linux/mman.h
index 8ddca62d6460..a842783ffa62 100644
--- a/include/linux/mman.h
+++ b/include/linux/mman.h
@@ -2,6 +2,7 @@
#ifndef _LINUX_MMAN_H
#define _LINUX_MMAN_H
+#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/percpu_counter.h>
@@ -94,7 +95,7 @@ static inline void vm_unacct_memory(long pages)
#endif
#ifndef arch_calc_vm_flag_bits
-#define arch_calc_vm_flag_bits(flags) 0
+#define arch_calc_vm_flag_bits(file, flags) 0
#endif
#ifndef arch_validate_prot
@@ -151,13 +152,13 @@ calc_vm_prot_bits(unsigned long prot, unsigned long pkey)
* Combine the mmap "flags" argument into "vm_flags" used internally.
*/
static inline unsigned long
-calc_vm_flag_bits(unsigned long flags)
+calc_vm_flag_bits(struct file *file, unsigned long flags)
{
return _calc_vm_trans(flags, MAP_GROWSDOWN, VM_GROWSDOWN ) |
_calc_vm_trans(flags, MAP_LOCKED, VM_LOCKED ) |
_calc_vm_trans(flags, MAP_SYNC, VM_SYNC ) |
_calc_vm_trans(flags, MAP_STACK, VM_NOHUGEPAGE) |
- arch_calc_vm_flag_bits(flags);
+ arch_calc_vm_flag_bits(file, flags);
}
unsigned long vm_commit_limit(void);
diff --git a/mm/mmap.c b/mm/mmap.c
index f102314bb500..f904b3bba962 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -344,7 +344,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
* to. we assume access permissions have been handled by the open
* of the memory object, so we don't do any here.
*/
- vm_flags |= calc_vm_prot_bits(prot, pkey) | calc_vm_flag_bits(flags) |
+ vm_flags |= calc_vm_prot_bits(prot, pkey) | calc_vm_flag_bits(file, flags) |
mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
/* Obtain the address to map to. we verify (or select) it and ensure
diff --git a/mm/nommu.c b/mm/nommu.c
index 635d028d647b..e9b5f527ab5b 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -842,7 +842,7 @@ static unsigned long determine_vm_flags(struct file *file,
{
unsigned long vm_flags;
- vm_flags = calc_vm_prot_bits(prot, 0) | calc_vm_flag_bits(flags);
+ vm_flags = calc_vm_prot_bits(prot, 0) | calc_vm_flag_bits(file, flags);
if (!file) {
/*
diff --git a/mm/shmem.c b/mm/shmem.c
index f24a0f34723e..ff194341fddb 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2737,9 +2737,6 @@ 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)
--
Catalin
