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

[Helge Deller <deller@gmx.de>]

* 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?

because it tries to map below TASK_UNMAPPED_BASE, for which (I assume) IA-64
has different aliasing/caching rules. There are some comments in the arch/ia64
files, but I'm not a IA-64 expert...

> * What happened to the offset_in_page check for other arches?

I thought it's not necessary.

But below is another (and much better) approach, which you may test.
I see quite some errors with the liburing testcases on hppa, but I think
they are not related to this function.

Can you test and report back?

Helge


From 457f2c2db984bc159119bfb4426d9dc6c2779ed6 Mon Sep 17 00:00:00 2001
From: Helge Deller <deller@gmx.de>
Date: Sun, 16 Jul 2023 08:45:17 +0200
Subject: [PATCH] io_uring: Adjust mapping wrt architecture aliasing
 requirements

When mapping memory to userspace use the architecture-provided
get_unmapped_area() function instead of the own copy which fails on
IA-64 since it doesn't allow mappings below TASK_UNMAPPED_BASE.

Additionally make sure to flag the requested memory as MAP_SHARED so
that any architecture-specific aliasing rules will be applied.

Reported-by: matoro <matoro_mailinglist_kernel@matoro.tk>
Signed-off-by: Helge Deller <deller@gmx.de>

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 3bca7a79efda..2e7dd93e45d0 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -3398,48 +3398,27 @@ 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.
+	 * aliasing rules of various architectures. Userspace is not able to
+	 * guess the offset address of kernel kmalloc()ed memory area.
 	 */
-	if (addr)
+	if (addr | (flags & MAP_FIXED))
 		return -EINVAL;

+	/*
+	 * The requested memory region is required to be shared between kernel
+	 * and userspace application.
+	 */
+	flags |= MAP_SHARED;
+
 	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;
+	return current->mm->get_unmapped_area(filp, addr, len, pgoff, flags);
 }

 #else /* !CONFIG_MMU */