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Message-ID: <ab636f4d-a140-460e-9ee4-fcd1e859ea67@suse.cz>
Date: Tue, 29 Oct 2024 08:50:11 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
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 10/28/24 23:14, Lorenzo Stoakes wrote:
> 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.
Consistently with the current implementation, which seems inconsiscent wrt
hugetlbfs.
> 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.
If it's confirmed to be oversight and MAP_SHARED hugetlbfs should be
allowed, we could add another is_file_hugepages() condition
> 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>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
> ---
> 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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