On Tue, Oct 29, 2024 at 6:04 AM Lorenzo Stoakes
<lorenzo.stoakes@xxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxx>
> Fixes: deb0f6562884 ("mm/mmap: undo ->mmap() when arch_validate_flags() fails")
> Cc: stable <stable@xxxxxxxxxx>
> Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
> Tested-by: Mark Brown <broonie@xxxxxxxxxx>
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
> ---
> 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;
Sorry for chiming in late. This looks problematic IIUC. The patch 5/5
moved arch_validate_flags() before call_mmap() as the commit log said.
But shmem_file() does this check:
mapping->a_ops == &shmem_aops
But mapping->a_ops is not initialized until shmem_mmap(), which is
called by call_mmap().
So shmem_file() should always return false here. Did I miss something?
> +
> + 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
>
