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

matoro
2023-07-12T04:59:23Z

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, 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?

$ git bisect log
git bisect start
# status: waiting for both good and bad commits
# good: [eceb0b18ae34b399856a2dd1eee8c18b2341e6f0] Linux 6.3.12
git bisect good eceb0b18ae34b399856a2dd1eee8c18b2341e6f0
# status: waiting for bad commit, 1 good commit known
# bad: [59377679473491963a599bfd51cc9877492312ee] Linux 6.4.1
git bisect bad 59377679473491963a599bfd51cc9877492312ee
# good: [457391b0380335d5e9a5babdec90ac53928b23b4] Linux 6.3
git bisect good 457391b0380335d5e9a5babdec90ac53928b23b4
# bad: [cb6fe2ceb667eb78f252d473b03deb23999ab1cf] Merge tag
'devicetree-for-6.4-2' of
git://git.kernel.org/pub/scm/linux/kernel/git/robh/linux
git bisect bad cb6fe2ceb667eb78f252d473b03deb23999ab1cf
# good: [f5468bec213ec2ad3f2724e3f1714b3bc7bf1515] Merge tag
'regmap-v6.4' of
git://git.kernel.org/pub/scm/linux/kernel/git/broonie/regmap
git bisect good f5468bec213ec2ad3f2724e3f1714b3bc7bf1515
# good: [207296f1a03bfead0110ffc4f192f242100ce4ff] netfilter: nf_tables:
allow to create netdev chain without device
git bisect good 207296f1a03bfead0110ffc4f192f242100ce4ff
# good: [85d7ab2463822a4ab096c0b7b59feec962552572] Merge tag
'for-6.4-tag' of
git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux
git bisect good 85d7ab2463822a4ab096c0b7b59feec962552572
# bad: [b68ee1c6131c540a62ecd443be89c406401df091] Merge tag 'scsi-misc'
of git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi
git bisect bad b68ee1c6131c540a62ecd443be89c406401df091
# bad: [48dc810012a6b4f4ba94073d6b7edb4f76edeb72] Merge tag
'for-6.4/dm-changes' of
git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm
git bisect bad 48dc810012a6b4f4ba94073d6b7edb4f76edeb72
# bad: [5b9a7bb72fddbc5247f56ede55d485fab7abdf92] Merge tag
'for-6.4/io_uring-2023-04-21' of git://git.kernel.dk/linux
git bisect bad 5b9a7bb72fddbc5247f56ede55d485fab7abdf92
# good: [5c7ecada25d2086aee607ff7deb69e77faa4aa92] Merge tag
'f2fs-for-6.4-rc1' of
git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs
git bisect good 5c7ecada25d2086aee607ff7deb69e77faa4aa92
# bad: [6e7248adf8f7adb5e36ec1e91efcc85a83bf8aeb] io_uring: refactor
io_cqring_wake()
git bisect bad 6e7248adf8f7adb5e36ec1e91efcc85a83bf8aeb
# bad: [2ad57931db641f3de627023afb8147a8ec0b41dc] io_uring: rename
trace_io_uring_submit_sqe() tracepoint
git bisect bad 2ad57931db641f3de627023afb8147a8ec0b41dc
# bad: [efba1a9e653e107577a48157b5424878c46f2285] io_uring: Move from
hlist to io_wq_work_node
git bisect bad efba1a9e653e107577a48157b5424878c46f2285
# bad: [ba56b63242d12df088ed9a701cad320e6b306dfe] io_uring/kbuf: move
pinning of provided buffer ring into helper
git bisect bad ba56b63242d12df088ed9a701cad320e6b306dfe
# good: [d4755e15386c38e4ae532ace5acc29fbfaee42e7] io_uring: avoid
hashing O_DIRECT writes if the filesystem doesn't need it
git bisect good d4755e15386c38e4ae532ace5acc29fbfaee42e7
# bad: [d808459b2e31bd5123a14258a7a529995db974c8] io_uring: Adjust
mapping wrt architecture aliasing requirements
git bisect bad d808459b2e31bd5123a14258a7a529995db974c8
# first bad commit: [d808459b2e31bd5123a14258a7a529995db974c8] io_uring:
Adjust mapping wrt architecture aliasing requirements