Re: [PATCH hotfix 6.12 v2 4/8] mm: resolve faulty mmap_region() error path behaviour
From: Catalin Marinas <catalin.marinas@arm.com>
Date: 2024-10-29 17:02:28
Also in:
linux-mm, lkml
Subsystem:
arm64 port (aarch64 architecture), memory management, memory mapping, parisc architecture, the rest, tmpfs (shmem filesystem) · Maintainers:
Catalin Marinas, Will Deacon, Andrew Morton, Liam R. Howlett, Lorenzo Stoakes, "James E.J. Bottomley", Helge Deller, Linus Torvalds, Hugh Dickins
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:quoted
On Tue, Oct 29, 2024 at 03:16:00PM +0000, Lorenzo Stoakes wrote:quoted
On Tue, Oct 29, 2024 at 03:04:41PM +0000, Catalin Marinas wrote:quoted
On Mon, Oct 28, 2024 at 10:14:50PM +0000, Lorenzo Stoakes wrote:quoted
So continue to check VM_MTE_ALLOWED which arch_calc_vm_flag_bits() sets if MAP_ANON.[...]quoted
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.quoted
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