From: Helge Deller <deller@gmx.de>
To: matoro <matoro_mailinglist_kernel@matoro.tk>
Cc: Jens Axboe <axboe@kernel.dk>,
io-uring@vger.kernel.org, Linux Ia64 <linux-ia64@vger.kernel.org>,
glaubitz@physik.fu-berlin.de, Sam James <sam@gentoo.org>
Subject: Re: [PATCH 1/5] io_uring: Adjust mapping wrt architecture aliasing requirements
Date: Wed, 12 Jul 2023 22:30:31 +0200 [thread overview]
Message-ID: <802b84f7-94f4-638b-3742-26bca00b262d@gmx.de> (raw)
In-Reply-To: <a3ae1656-be97-ccc2-8962-1cb70ebc67fa@gmx.de>
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
next prev parent reply other threads:[~2023-07-12 20:31 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20230314171641.10542-1-axboe@kernel.dk>
[not found] ` <20230314171641.10542-2-axboe@kernel.dk>
2023-07-12 4:43 ` [PATCH 1/5] io_uring: Adjust mapping wrt architecture aliasing requirements matoro
2023-07-12 16:24 ` Helge Deller
2023-07-12 17:28 ` matoro
2023-07-12 19:05 ` Helge Deller
2023-07-12 20:30 ` Helge Deller [this message]
2023-07-13 0:35 ` matoro
2023-07-13 7:27 ` Helge Deller
2023-07-13 23:57 ` matoro
2023-07-16 6:54 ` Helge Deller
2023-07-16 18:03 ` matoro
2023-07-16 20:54 ` Helge Deller
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