Re: [PATCH 1/5] io_uring: Adjust mapping wrt architecture aliasing requirements

[matoro <matoro_mailinglist_kernel@matoro.tk>]

On 2023-07-13 03:27, Helge Deller wrote:
> * matoro <matoro_mailinglist_kernel@matoro.tk>:
>> On 2023-07-12 16:30, Helge Deller wrote:
>> > On 7/12/23 21:05, Helge Deller wrote:
>> > > On 7/12/23 19:28, matoro wrote:
>> > > > On 2023-07-12 12:24, Helge Deller wrote:
>> > > > > Hi Matoro,
>> > > > >
>> > > > > * matoro <matoro_mailinglist_kernel@matoro.tk>:
>> > > > > > On 2023-03-14 13:16, Jens Axboe wrote:
>> > > > > > > From: Helge Deller <deller@gmx.de>
>> > > > > > >
>> > > > > > > Some architectures have memory cache aliasing requirements (e.g. parisc)
>> > > > > > > if memory is shared between userspace and kernel. This patch fixes the
>> > > > > > > kernel to return an aliased address when asked by userspace via mmap().
>> > > > > > >
>> > > > > > > Signed-off-by: Helge Deller <deller@gmx.de>
>> > > > > > > Signed-off-by: Jens Axboe <axboe@kernel.dk>
>> > > > > > > ---
>> > > > > > >  io_uring/io_uring.c | 51 +++++++++++++++++++++++++++++++++++++++++++++
>> > > > > > >  1 file changed, 51 insertions(+)
>> > > > > > >
>> > > > > > > diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
>> > > > > > > index 722624b6d0dc..3adecebbac71 100644
>> > > > > > > --- a/io_uring/io_uring.c
>> > > > > > > +++ b/io_uring/io_uring.c
>> > > > > > > @@ -72,6 +72,7 @@
>> > > > > > >  #include <linux/io_uring.h>
>> > > > > > >  #include <linux/audit.h>
>> > > > > > >  #include <linux/security.h>
>> > > > > > > +#include <asm/shmparam.h>
>> > > > > > >
>> > > > > > >  #define CREATE_TRACE_POINTS
>> > > > > > >  #include <trace/events/io_uring.h>
>> > > > > > > @@ -3317,6 +3318,54 @@ static __cold int io_uring_mmap(struct file
>> > > > > > > *file, struct vm_area_struct *vma)
>> > > > > > >      return remap_pfn_range(vma, vma->vm_start, pfn, sz,
>> > > > > > > vma->vm_page_prot);
>> > > > > > >  }
>> > > > > > >
>> > > > > > > +static unsigned long io_uring_mmu_get_unmapped_area(struct file *filp,
>> > > > > > > +            unsigned long addr, unsigned long len,
>> > > > > > > +            unsigned long pgoff, unsigned long flags)
>> > > > > > > +{
>> > > > > > > +    const unsigned long mmap_end = arch_get_mmap_end(addr, len, flags);
>> > > > > > > +    struct vm_unmapped_area_info info;
>> > > > > > > +    void *ptr;
>> > > > > > > +
>> > > > > > > +    /*
>> > > > > > > +     * Do not allow to map to user-provided address to avoid breaking the
>> > > > > > > +     * aliasing rules. Userspace is not able to guess the offset address
>> > > > > > > of
>> > > > > > > +     * kernel kmalloc()ed memory area.
>> > > > > > > +     */
>> > > > > > > +    if (addr)
>> > > > > > > +        return -EINVAL;
>> > > > > > > +
>> > > > > > > +    ptr = io_uring_validate_mmap_request(filp, pgoff, len);
>> > > > > > > +    if (IS_ERR(ptr))
>> > > > > > > +        return -ENOMEM;
>> > > > > > > +
>> > > > > > > +    info.flags = VM_UNMAPPED_AREA_TOPDOWN;
>> > > > > > > +    info.length = len;
>> > > > > > > +    info.low_limit = max(PAGE_SIZE, mmap_min_addr);
>> > > > > > > +    info.high_limit = arch_get_mmap_base(addr, current->mm->mmap_base);
>> > > > > > > +#ifdef SHM_COLOUR
>> > > > > > > +    info.align_mask = PAGE_MASK & (SHM_COLOUR - 1UL);
>> > > > > > > +#else
>> > > > > > > +    info.align_mask = PAGE_MASK & (SHMLBA - 1UL);
>> > > > > > > +#endif
>> > > > > > > +    info.align_offset = (unsigned long) ptr;
>> > > > > > > +
>> > > > > > > +    /*
>> > > > > > > +     * A failed mmap() very likely causes application failure,
>> > > > > > > +     * so fall back to the bottom-up function here. This scenario
>> > > > > > > +     * can happen with large stack limits and large mmap()
>> > > > > > > +     * allocations.
>> > > > > > > +     */
>> > > > > > > +    addr = vm_unmapped_area(&info);
>> > > > > > > +    if (offset_in_page(addr)) {
>> > > > > > > +        info.flags = 0;
>> > > > > > > +        info.low_limit = TASK_UNMAPPED_BASE;
>> > > > > > > +        info.high_limit = mmap_end;
>> > > > > > > +        addr = vm_unmapped_area(&info);
>> > > > > > > +    }
>> > > > > > > +
>> > > > > > > +    return addr;
>> > > > > > > +}
>> > > > > > > +
>> > > > > > >  #else /* !CONFIG_MMU */
>> > > > > > >
>> > > > > > >  static int io_uring_mmap(struct file *file, struct vm_area_struct *vma)
>> > > > > > > @@ -3529,6 +3578,8 @@ static const struct file_operations io_uring_fops
>> > > > > > > = {
>> > > > > > >  #ifndef CONFIG_MMU
>> > > > > > >      .get_unmapped_area = io_uring_nommu_get_unmapped_area,
>> > > > > > >      .mmap_capabilities = io_uring_nommu_mmap_capabilities,
>> > > > > > > +#else
>> > > > > > > +    .get_unmapped_area = io_uring_mmu_get_unmapped_area,
>> > > > > > >  #endif
>> > > > > > >      .poll        = io_uring_poll,
>> > > > > > >  #ifdef CONFIG_PROC_FS
>> > > > > >
>> > > > > > Hi Jens, Helge - I've bisected a regression with
>> > > > > > io_uring on ia64 to this
>> > > > > > patch in 6.4.  Unfortunately this breaks userspace
>> > > > > > programs using io_uring,
>> > > > > > the easiest one to test is cmake with an io_uring
>> > > > > > enabled libuv (i.e., libuv
>> > > > > > >= 1.45.0) which will hang.
>> > > > > >
>> > > > > > I am aware that ia64 is in a vulnerable place right now
>> > > > > > which I why I am
>> > > > > > keeping this spread limited.  Since this clearly involves
>> > > > > > architecture-specific changes for parisc,
>> > > > >
>> > > > > it isn't so much architecture-specific... (just one ifdef)
>> > > > >
>> > > > > > is there any chance of looking at
>> > > > > > what is required to do the same for ia64?  I looked at
>> > > > > > 0ef36bd2b37815719e31a72d2beecc28ca8ecd26 ("parisc:
>> > > > > > change value of SHMLBA
>> > > > > > from 0x00400000 to PAGE_SIZE") and tried to replicate the SHMLBA ->
>> > > > > > SHM_COLOUR change, but it made no difference.
>> > > > > >
>> > > > > > If hardware is necessary for testing, I can provide it,
>> > > > > > including remote BMC
>> > > > > > access for restarts/kernel debugging.  Any takers?
>> > > > >
>> > > > > I won't have time to test myself, but maybe you could test?
>> > > > >
>> > > > > Basically we should try to find out why
>> > > > > io_uring_mmu_get_unmapped_area()
>> > > > > doesn't return valid addresses, while arch_get_unmapped_area()
>> > > > > [in arch/ia64/kernel/sys_ia64.c] does.
>> > > > >
>> > > > > You could apply this patch first:
>> > > > > It introduces a memory leak (as it requests memory twice),
>> > > > > but maybe we
>> > > > > get an idea?
>> > > > > The ia64 arch_get_unmapped_area() searches for memory from bottom
>> > > > > (flags=0), while io_uring function tries top-down first.
>> > > > > Maybe that's
>> > > > > the problem. And I don't understand the offset_in_page() check right
>> > > > > now.
>> > > > >
>> > > > > diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
>> > > > > index 3bca7a79efda..93b1964d2bbb 100644
>> > > > > --- a/io_uring/io_uring.c
>> > > > > +++ b/io_uring/io_uring.c
>> > > > > @@ -3431,13 +3431,17 @@ static unsigned long
>> > > > > io_uring_mmu_get_unmapped_area(struct file *filp,
>> > > > >       * can happen with large stack limits and large mmap()
>> > > > >       * allocations.
>> > > > >       */
>> > > > > +/* compare to arch_get_unmapped_area() in
>> > > > > arch/ia64/kernel/sys_ia64.c */
>> > > > >      addr = vm_unmapped_area(&info);
>> > > > > -    if (offset_in_page(addr)) {
>> > > > > +printk("io_uring_mmu_get_unmapped_area() address 1 is:
>> > > > > %px\n", addr);
>> > > > > +    addr = NULL;
>> > > > > +    if (!addr) {
>> > > > >          info.flags = 0;
>> > > > >          info.low_limit = TASK_UNMAPPED_BASE;
>> > > > >          info.high_limit = mmap_end;
>> > > > >          addr = vm_unmapped_area(&info);
>> > > > >      }
>> > > > > +printk("io_uring_mmu_get_unmapped_area() returns address
>> > > > > %px\n", addr);
>> > > > >
>> > > > >      return addr;
>> > > > >  }
>> > > > >
>> > > > >
>> > > > > Another option is to disable the call to
>> > > > > io_uring_nommu_get_unmapped_area())
>> > > > > with the next patch. Maybe you could add printks() to ia64's
>> > > > > arch_get_unmapped_area()
>> > > > > and check what it returns there?
>> > > > >
>> > > > > @@ -3654,6 +3658,8 @@ static const struct file_operations
>> > > > > io_uring_fops = {
>> > > > >  #ifndef CONFIG_MMU
>> > > > >      .get_unmapped_area = io_uring_nommu_get_unmapped_area,
>> > > > >      .mmap_capabilities = io_uring_nommu_mmap_capabilities,
>> > > > > +#elif 0    /* IS_ENABLED(CONFIG_IA64) */
>> > > > > +    .get_unmapped_area = NULL,
>> > > > >  #else
>> > > > >      .get_unmapped_area = io_uring_mmu_get_unmapped_area,
>> > > > >  #endif
>> > > > >
>> > > > > Helge
>> > > >
>> > > > Thanks Helge.  Sample output from that first patch:
>> > > >
>> > > > [Wed Jul 12 13:09:50 2023] io_uring_mmu_get_unmapped_area()
>> > > > address 1 is: 1ffffffffff40000
>> > > > [Wed Jul 12 13:09:50 2023] io_uring_mmu_get_unmapped_area()
>> > > > returns address 2000000001e40000
>> > > > [Wed Jul 12 13:09:50 2023] io_uring_mmu_get_unmapped_area()
>> > > > address 1 is: 1ffffffffff20000
>> > > > [Wed Jul 12 13:09:50 2023] io_uring_mmu_get_unmapped_area()
>> > > > returns address 2000000001f20000
>> > > > [Wed Jul 12 13:09:50 2023] io_uring_mmu_get_unmapped_area()
>> > > > address 1 is: 1ffffffffff30000
>> > > > [Wed Jul 12 13:09:50 2023] io_uring_mmu_get_unmapped_area()
>> > > > returns address 2000000001f30000
>> > > > [Wed Jul 12 13:09:50 2023] io_uring_mmu_get_unmapped_area()
>> > > > address 1 is: 1ffffffffff90000
>> > > > [Wed Jul 12 13:09:50 2023] io_uring_mmu_get_unmapped_area()
>> > > > returns address 2000000001f90000
>> > > >
>> > > > This pattern seems to be pretty stable, I tried instead just
>> > > > directly returning the result of a call to
>> > > > arch_get_unmapped_area() at the end of the function and it seems
>> > > > similar:
>> > > >
>> > > > [Wed Jul 12 13:27:07 2023] io_uring_mmu_get_unmapped_area()
>> > > > would return address 1ffffffffffd0000
>> > > > [Wed Jul 12 13:27:07 2023] but arch_get_unmapped_area() would
>> > > > return address 2000000001f00000
>> > > > [Wed Jul 12 13:27:07 2023] io_uring_mmu_get_unmapped_area()
>> > > > would return address 1ffffffffff00000
>> > > > [Wed Jul 12 13:27:07 2023] but arch_get_unmapped_area() would
>> > > > return address 1ffffffffff00000
>> > > > [Wed Jul 12 13:27:07 2023] io_uring_mmu_get_unmapped_area()
>> > > > would return address 1fffffffffe20000
>> > > > [Wed Jul 12 13:27:07 2023] but arch_get_unmapped_area() would
>> > > > return address 2000000002000000
>> > > > [Wed Jul 12 13:27:07 2023] io_uring_mmu_get_unmapped_area()
>> > > > would return address 1fffffffffe30000
>> > > > [Wed Jul 12 13:27:07 2023] but arch_get_unmapped_area() would
>> > > > return address 2000000002100000
>> > > >
>> > > > Is that enough of a clue to go on?
>> > >
>> > > SHMLBA on ia64 is 0x100000:
>> > > arch/ia64/include/asm/shmparam.h:#define        SHMLBA  (1024*1024)
>> > > but the values returned by io_uring_mmu_get_unmapped_area() does not
>> > > fullfill this.
>> > >
>> > > So, probably ia64's SHMLBA isn't pulled in correctly in
>> > > io_uring/io_uring.c.
>> > > Check value of this line:
>> > >      info.align_mask = PAGE_MASK & (SHMLBA - 1UL);
>> > >
>> > > You could also add
>> > > #define SHM_COLOUR  0x100000
>> > > in front of the
>> > >      #ifdef SHM_COLOUR
>> > > (define SHM_COLOUR in io_uring/kbuf.c too).
>> >
>> > What is the value of PAGE_SIZE and "ptr" on your machine?
>> > For 4k page size I get:
>> > SHMLBA -1   ->        FFFFF
>> > PAGE_MASK   -> FFFFFFFFF000
>> > so,
>> > info.align_mask = PAGE_MASK & (SHMLBA - 1UL) = 0xFF000;
>> > You could try to set nfo.align_mask = 0xfffff;
>> >
>> > Helge
>> 
>> Using 64KiB (65536) PAGE_SIZE here.  64-bit pointers.
>> 
>> Tried both #define SHM_COLOUR 0x100000, as well and info.align_mask =
>> 0xFFFFF, but both of them made the problem change from 100% 
>> reproducible, to
>> intermittent.
>> 
>> After inspecting the ouput I observed that it hangs only when the 
>> first
>> allocation returns an address below 0x2000000000000000, and the second
>> returns an address above it.  When both addresses are above it, it 
>> does not
>> hang.  Examples:
>> 
>> When it works:
>> $ cmake --version
>> cmake version 3.26.4
>> 
>> CMake suite maintained and supported by Kitware (kitware.com/cmake).
>> $ dmesg --color=always -T | tail -n 4
>> [Wed Jul 12 20:32:37 2023] io_uring_mmu_get_unmapped_area() would 
>> return
>> address 1fffffffffe20000
>> [Wed Jul 12 20:32:37 2023] but arch_get_unmapped_area() would return 
>> address
>> 2000000002000000
>> [Wed Jul 12 20:32:37 2023] io_uring_mmu_get_unmapped_area() would 
>> return
>> address 1fffffffffe50000
>> [Wed Jul 12 20:32:37 2023] but arch_get_unmapped_area() would return 
>> address
>> 2000000002100000
>> 
>> 
>> When it hangs:
>> $ cmake --version
>> cmake version 3.26.4
>> 
>> CMake suite maintained and supported by Kitware (kitware.com/cmake).
>> ^C
>> $ dmesg --color=always -T | tail -n 4
>> [Wed Jul 12 20:33:12 2023] io_uring_mmu_get_unmapped_area() would 
>> return
>> address 1ffffffffff00000
>> [Wed Jul 12 20:33:12 2023] but arch_get_unmapped_area() would return 
>> address
>> 1ffffffffff00000
>> [Wed Jul 12 20:33:12 2023] io_uring_mmu_get_unmapped_area() would 
>> return
>> address 1fffffffffe60000
>> [Wed Jul 12 20:33:12 2023] but arch_get_unmapped_area() would return 
>> address
>> 2000000001f00000
>> 
>> Is io_uring_mmu_get_unmapped_area supported to always return addresses 
>> above
>> 0x2000000000000000?
> 
> Yes, with the patch below.
> 
>> Any reason why it is not doing so sometimes?
> 
> It depends on the parameters for vm_unmapped_area(). Specifically
> info.flags=0.
> 
> Try this patch:
> 
> diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
> index 3bca7a79efda..b259794ab53b 100644
> --- a/io_uring/io_uring.c
> +++ b/io_uring/io_uring.c
> @@ -3429,10 +3429,13 @@ static unsigned long 
> io_uring_mmu_get_unmapped_area(struct file *filp,
>  	 * A failed mmap() very likely causes application failure,
>  	 * so fall back to the bottom-up function here. This scenario
>  	 * can happen with large stack limits and large mmap()
> -	 * allocations.
> +	 * allocations. Use bottom-up on IA64 for correct aliasing.
>  	 */
> -	addr = vm_unmapped_area(&info);
> -	if (offset_in_page(addr)) {
> +	if (IS_ENABLED(CONFIG_IA64))
> +		addr = NULL;
> +	else
> +		addr = vm_unmapped_area(&info);
> +	if (!addr) {
>  		info.flags = 0;
>  		info.low_limit = TASK_UNMAPPED_BASE;
>  		info.high_limit = mmap_end;
> 
> Helge

This patch does do the trick, but I am a little unsure if it's the right 
one to go in:

* Adding an arch-specific conditional feels like a bad hack, why is it 
not working with the other vm_unmapped_area_info settings?
* What happened to the offset_in_page check for other arches?