Re: [PATCH 4/5] hurd: Fix mapping at address 0 with MAP_FIXED

[Samuel Thibault]

Applied, thanks!

Sergey Bugaev, le lun. 26 juin 2023 02:17:50 +0300, a ecrit:
> Zero address passed to mmap () typically means the caller doesn't have
> any specific preferred address. Not so if MAP_FIXED is passed: in this
> case 0 means literal 0. Fix this case to pass anywhere = 0 into vm_map.
> 
> Also add some documentation.
> 
> Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
> ---
>  sysdeps/mach/hurd/mmap.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/sysdeps/mach/hurd/mmap.c b/sysdeps/mach/hurd/mmap.c
> index 5aa70083..33672cf6 100644
> --- a/sysdeps/mach/hurd/mmap.c
> +++ b/sysdeps/mach/hurd/mmap.c
> @@ -38,7 +38,7 @@ __mmap (void *addr, size_t len, int prot, int flags, int 
> fd, off_t offset)
>    vm_prot_t vmprot, max_vmprot;
>    memory_object_t memobj;
>    vm_address_t mapaddr, mask;
> -  boolean_t copy;
> +  boolean_t copy, anywhere;
>  
>    mapaddr = (vm_address_t) addr;
>  
> @@ -55,6 +55,7 @@ __mmap (void *addr, size_t len, int prot, int flags, int 
> fd, off_t offset)
>      vmprot |= VM_PROT_EXECUTE;
>  
>    copy = ! (flags & MAP_SHARED);
> +  anywhere = ! (flags & MAP_FIXED);
>  
>  #ifdef __LP64__
>    if ((addr == NULL) && (prot & PROT_EXEC)
> @@ -141,9 +142,12 @@ __mmap (void *addr, size_t len, int prot, int flags, int 
> fd, off_t offset)
>    if (copy)
>      max_vmprot = VM_PROT_ALL;
>  
> +  /* When ANYWHERE is true but the caller has provided a preferred address,
> +     try mapping at that address with anywhere = 0 first.  If this fails,
> +     we'll retry with anywhere = 1 below.  */
>    err = __vm_map (__mach_task_self (),
>                 &mapaddr, (vm_size_t) len, mask,
> -               mapaddr == 0,
> +               anywhere && (mapaddr == 0),
>                 memobj, (vm_offset_t) offset,
>                 copy, vmprot, max_vmprot,
>                 copy ? VM_INHERIT_COPY : VM_INHERIT_SHARE);
> @@ -165,7 +169,10 @@ __mmap (void *addr, size_t len, int prot, int flags, int 
> fd, off_t offset)
>      }
>    else
>      {
> +      /* This mmap call is allowed to allocate anywhere,  */
>        if (mapaddr != 0 && (err == KERN_NO_SPACE || err == 
> KERN_INVALID_ADDRESS))
> +        /* ...but above, we tried allocating at the specific address,
> +           and failed to.  Now try again, with anywhere = 1 this time.  */
>       err = __vm_map (__mach_task_self (),
>                       &mapaddr, (vm_size_t) len, mask,
>                       1, memobj, (vm_offset_t) offset,
> -- 
> 2.41.0
> 
> 

-- 
Samuel
---
Pour une évaluation indépendante, transparente et rigoureuse !
Je soutiens la Commission d'Évaluation de l'Inria.