[6.1.y,v2,3/4] mm: refactor arch_calc_vm_flag_bits() and arm64 MTE handling

Commit Message

Lorenzo Stoakes Nov. 18, 2024, 4:17 p.m. UTC

[ Upstream commit 5baf8b037debf4ec60108ccfeccb8636d1dbad81 ]

Currently MTE is permitted in two circumstances (desiring to use MTE
having been specified by the VM_MTE flag) - where MAP_ANONYMOUS is
specified, as checked by arch_calc_vm_flag_bits() and actualised by
setting the VM_MTE_ALLOWED flag, or if the file backing the mapping is
shmem, in which case we set VM_MTE_ALLOWED in shmem_mmap() when the mmap
hook is activated in mmap_region().

The function that checks that, if VM_MTE is set, VM_MTE_ALLOWED is also
set is the arm64 implementation of arch_validate_flags().

Unfortunately, we intend to refactor mmap_region() to perform this check
earlier, meaning that in the case of a shmem backing we will not have
invoked shmem_mmap() yet, causing the mapping to fail spuriously.

It is inappropriate to set this architecture-specific flag in general mm
code anyway, so a sensible resolution of this issue is to instead move the
check somewhere else.

We resolve this by setting VM_MTE_ALLOWED much earlier in do_mmap(), via
the arch_calc_vm_flag_bits() call.

This is an appropriate place to do this as we already check for the
MAP_ANONYMOUS case here, and the shmem file case is simply a variant of
the same idea - we permit RAM-backed memory.

This requires a modification to the arch_calc_vm_flag_bits() signature to
pass in a pointer to the struct file associated with the mapping, however
this is not too egregious as this is only used by two architectures anyway
- arm64 and parisc.

So this patch performs this adjustment and removes the unnecessary
assignment of VM_MTE_ALLOWED in shmem_mmap().

[[e-mail]: fix whitespace, per Catalin]
Link: https://lkml.kernel.org/r/ec251b2[e-mail]
Fixes: deb0f6562884 ("mm/mmap: undo ->mmap() when arch_validate_flags() fails")
Signed-off-by: Lorenzo Stoakes <[e-mail]>
Suggested-by: Catalin Marinas <[e-mail]>
Reported-by: Jann Horn <[e-mail]>
Reviewed-by: Catalin Marinas <[e-mail]>
Reviewed-by: Vlastimil Babka <[e-mail]>
Cc: Andreas Larsson <[e-mail]>
Cc: David S. Miller <[e-mail]>
Cc: Helge Deller <[e-mail]>
Cc: James E.J. Bottomley <[e-mail]>
Cc: Liam R. Howlett <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Mark Brown <[e-mail]>
Cc: Peter Xu <[e-mail]>
Cc: Will Deacon <[e-mail]>
Cc: <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Lorenzo Stoakes <[e-mail]>
---
 arch/arm64/include/asm/mman.h | 10 +++++++---
 include/linux/mman.h          |  7 ++++---
 mm/mmap.c                     |  2 +-
 mm/nommu.c                    |  2 +-
 mm/shmem.c                    |  3 ---
 5 files changed, 13 insertions(+), 11 deletions(-)

Patch

diff --git a/arch/arm64/include/asm/mman.h b/arch/arm64/include/asm/mman.h
index 5966ee4a6154..ef35c52aabd6 100644
--- a/arch/arm64/include/asm/mman.h
+++ b/arch/arm64/include/asm/mman.h
@@ -3,6 +3,8 @@ 
 #define __ASM_MMAN_H__
 
 #include <linux/compiler.h>
+#include <linux/fs.h>
+#include <linux/shmem_fs.h>
 #include <linux/types.h>
 #include <uapi/asm/mman.h>
 
@@ -21,19 +23,21 @@  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
 	 * backed by tags-capable memory. The vm_flags may be overridden by a
 	 * filesystem supporting MTE (RAM-based).
 	 */
-	if (system_supports_mte() && (flags & MAP_ANONYMOUS))
+	if (system_supports_mte() &&
+	    ((flags & MAP_ANONYMOUS) || 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/include/linux/mman.h b/include/linux/mman.h
index 58b3abd457a3..21ea08b919d9 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>
 
@@ -90,7 +91,7 @@  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
@@ -147,12 +148,12 @@  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      ) |
-	       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 4bfec4df51c2..322677f61d30 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1316,7 +1316,7 @@  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;
 
 	if (flags & MAP_LOCKED)
diff --git a/mm/nommu.c b/mm/nommu.c
index e0428fa57526..859ba6bdeb9c 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -903,7 +903,7 @@  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);
 	/* vm_flags |= mm->def_flags; */
 
 	if (!(capabilities & NOMMU_MAP_DIRECT)) {
diff --git a/mm/shmem.c b/mm/shmem.c
index 0e1fbc53717d..d1a33f66cc7f 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2308,9 +2308,6 @@  static int shmem_mmap(struct file *file, struct vm_area_struct *vma)
 	if (ret)
 		return ret;
 
-	/* arm64 - allow memory tagging on RAM-based files */
-	vma->vm_flags |= VM_MTE_ALLOWED;
-
 	file_accessed(file);
 	vma->vm_ops = &shmem_vm_ops;
 	return 0;