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Message-ID: <ea10a05be83c70cf610d470fe3b4c05513e3859c.1730206735.git.lorenzo.stoakes@oracle.com>
Date: Tue, 29 Oct 2024 13:03:46 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Xu <peterx@...hat.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Mark Brown <broonie@...nel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Andreas Larsson <andreas@...sler.com>
Subject: [PATCH hotfix 6.12 v3 4/5] mm: refactor arch_validate_flags() and arm64 MTE handling

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 to arch_validate_flags() itself.

This requires a modification to the arch_validate_flags() 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 sparc.

So this patch performs this adjustment and moves the check to
arch_validate_flags() which resolves the issue.

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.

Reported-by: Jann Horn <jannh@...gle.com>
Fixes: deb0f6562884 ("mm/mmap: undo ->mmap() when arch_validate_flags() fails")
Cc: stable <stable@...nel.org>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
Tested-by: Mark Brown <broonie@...nel.org>
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
---
 arch/arm64/include/asm/mman.h | 29 +++++++++++++++++++++++++----
 arch/sparc/include/asm/mman.h |  5 +++--
 include/linux/mman.h          |  2 +-
 mm/mmap.c                     |  2 +-
 mm/mprotect.c                 |  2 +-
 mm/shmem.c                    |  3 ---
 6 files changed, 31 insertions(+), 12 deletions(-)

diff --git a/arch/arm64/include/asm/mman.h b/arch/arm64/include/asm/mman.h
index 9e39217b4afb..94925a0482e3 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 +62,34 @@ 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;
+
+	/*
+	 * We explicitly permit MAP_ANONYMOUS and shmem backed mappings to use
+	 * MTE. We check for shmem explicitly here.
+	 *
+	 * The MAP_ANONYMOUS case is handled by arch_calc_vm_flag_bits() which
+	 * explicitly sets VM_MTE_ALLOWED which we check for here also.
+	 *
+	 * Ideally we'd perform both checks here but existing semantics support
+	 * hugetlb in MAP_ANONYMOUS mode but not a MAP_SHARED mapping, which is
+	 * likely unintended but we maintain identical behaviour for
+	 * consistency.
+	 */
+	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 ab71d4c3464c..40b5858ae875 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1511,7 +1511,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 	}

 	/* Allow architectures to sanity-check the vm_flags */
-	if (!arch_validate_flags(vma->vm_flags)) {
+	if (!arch_validate_flags(file, vma->vm_flags)) {
 		error = -EINVAL;
 		goto close_and_free_vma;
 	}
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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