Re: [PATCH 1/5] io_uring: Adjust mapping wrt architecture aliasing requirements
matoro <[email protected]>
| Newsgroups | gmane.linux.ports.ia64,gmane.linux.kernel.io-uring |
|---|---|
| Message-ID | <[email protected]> |
On 2023-07-13 03:27, Helge Deller wrote: > * matoro <[email protected]>: >> 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 <[email protected]>: >> > > > > > On 2023-03-14 13:16, Jens Axboe wrote: >> > > > > > > From: Helge Deller <[email protected]> >> > > > > > > >> > > > > > > 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 <[email protected]> >> > > > > > > Signed-off-by: Jens Axboe <[email protected]> >> > > > > > > --- >> > > > > > > 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?