Message-ID: <Zjt3Apr8ILFA4oK_@fedora>
Date: Wed, 8 May 2024 08:58:42 -0400
From: Audra Mitchell <audra@...hat.com>
To: David Hildenbrand <david@...hat.com>
Cc: viro@...iv.linux.org.uk, brauner@...nel.org, jack@...e.cz,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, shuah@...nel.org,
	linux-kselftest@...r.kernel.org, linux-mm@...ck.org,
	raquini@...hat.com, Peter Xu <peterx@...hat.com>
Subject: Re: [PATCH 1/2] Fix userfaultfd_api to return EINVAL as expected

On Wed, May 08, 2024 at 09:39:10AM +0200, David Hildenbrand wrote:
> On 07.05.24 21:55, Audra Mitchell wrote:
> > Currently if we request a feature that is not set in the Kernel
> > config we fail silently and return the available features. However, the
> > documentation indicates we should return an EINVAL.
> 
> I assume you are referencing
> 
> "EINVAL The API version requested in the api field is not supported by this
> kernel, or  the  features  field passed to the kernel includes feature bits
> that are not supported by the current kernel version."
> 
> and
> 
> "To  enable  userfaultfd features the application should set a bit
> corresponding to each feature it wants to enable in the features field. If
> the kernel supports all the requested features it will enable them.
> Otherwise it will zero out the returned uffdio_api structure and return
> EINVAL.
> "
> 
> in which case I agree.

Yep! I'm referencing the man page.

> 
> > 
> > We need to fix this issue since we can end up with a Kernel warning
> > should a program request the feature UFFD_FEATURE_WP_UNPOPULATED on
> > a kernel with the config not set with this feature.
> 
> Can you mention which exact one? Is it a WARN* or a pr_warn() ?

Here is the kernel warning I get:

[  200.803094] unrecognized swap entry 0x7c00000000000001
[  200.808270] ------------[ cut here ]------------
[  200.812896] WARNING: CPU: 91 PID: 13634 at mm/memory.c:1660 zap_pte_range+0x43d/0x660
[  200.820738] Modules linked in: qrtr bridge stp llc rfkill sunrpc amd_atl intel_rapl_msr intel_rapl_common amd64_edac edac_mce_amd kvm_amd kvm ipmi_ssif acpi_ipmi i2c_piix4 ipmi_si wmi_bmof dcdbas dell_smbios dell_wmi_descriptor ptdma ipmi_devintf rapl ipmi_msghandler acpi_power_meter pcspkr k10temp xfs libcrc32c sd_mod t10_pi mgag200 sg drm_kms_helper crct10dif_pclmul i2c_algo_bit ahci crc32_pclmul drm_shmem_helper libahci crc32c_intel drm i40e libata ghash_clmulni_intel tg3 ccp megaraid_sas sp5100_tco wmi dm_mirror dm_region_hash dm_log dm_mod fuse
[  200.869387] CPU: 91 PID: 13634 Comm: userfaultfd Kdump: loaded Not tainted 6.9.0-rc5+ #8
[  200.877477] Hardware name: Dell Inc. PowerEdge R6525/0N7YGH, BIOS 2.7.3 03/30/2022
[  200.885052] RIP: 0010:zap_pte_range+0x43d/0x660
[  200.889595] Code: 83 fa 02 0f 86 44 01 00 00 83 f9 17 0f 84 e1 00 00 00 83 f9 1f 0f 84 d0 00 00 00 48 89 c6 48 c7 c7 00 e4 dd bb e8 73 a2 de ff <0f> 0b e9 44 fd ff ff 45 0f b6 44 24 20 41 f6 c0 f4 75 27 4c 89 ee
[  200.908348] RSP: 0018:ffffa18d2e6c37c8 EFLAGS: 00010246
[  200.913584] RAX: 000000000000002a RBX: 00007f26d3600000 RCX: 0000000000000000
[  200.920730] RDX: 0000000000000000 RSI: ffff93503f9a0bc0 RDI: ffff93503f9a0bc0
[  200.927867] RBP: 00007f26d35cc000 R08: 0000000000000000 R09: ffffa18d2e6c3688
[  200.935009] R10: ffffa18d2e6c3680 R11: ffffffffbc9de448 R12: ffffa18d2e6c39e8
[  200.942149] R13: ffff92d1ebc15b50 R14: ffff93114e0cde60 R15: ffffa18d2e6c3928
[  200.949291] FS:  0000000000000000(0000) GS:ffff93503f980000(0000) knlGS:0000000000000000
[  200.957384] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  200.963140] CR2: 00007f26b1600658 CR3: 00000040905ba000 CR4: 0000000000350ef0
[  200.970283] Call Trace:
[  200.972745]  <TASK>
[  200.974862]  ? __warn+0x7f/0x130
[  200.978108]  ? zap_pte_range+0x43d/0x660
[  200.982044]  ? report_bug+0x18a/0x1a0
[  200.985720]  ? handle_bug+0x3c/0x70
[  200.989219]  ? exc_invalid_op+0x14/0x70
[  200.993068]  ? asm_exc_invalid_op+0x16/0x20
[  200.997265]  ? zap_pte_range+0x43d/0x660
[  201.001199]  ? zap_pte_range+0x43d/0x660
[  201.005134]  zap_pmd_range.isra.0+0xf9/0x230
[  201.009416]  unmap_page_range+0x2d4/0x4a0
[  201.013436]  unmap_vmas+0xa8/0x180
[  201.016854]  exit_mmap+0xea/0x3b0
[  201.020191]  __mmput+0x43/0x120
[  201.023342]  exit_mm+0xb1/0x110
[  201.026496]  do_exit+0x270/0x4f0
[  201.029739]  do_group_exit+0x2c/0x80
[  201.033326]  get_signal+0x886/0x8b0
[  201.036828]  ? srso_return_thunk+0x5/0x5f
[  201.040848]  arch_do_signal_or_restart+0x25/0x100
[  201.045563]  ? srso_return_thunk+0x5/0x5f
[  201.049583]  ? vma_set_page_prot+0x5e/0xc0
[  201.053692]  ? srso_return_thunk+0x5/0x5f
[  201.057713]  ? syscall_exit_work+0xff/0x130
[  201.061908]  syscall_exit_to_user_mode+0x1b3/0x200
[  201.066712]  do_syscall_64+0x87/0x160
[  201.070387]  ? srso_return_thunk+0x5/0x5f
[  201.074405]  ? do_mmap+0x416/0x5f0
[  201.077821]  ? srso_return_thunk+0x5/0x5f
[  201.081840]  ? rseq_get_rseq_cs+0x1d/0x240
[  201.085950]  ? srso_return_thunk+0x5/0x5f
[  201.089970]  ? rseq_ip_fixup+0x6d/0x1d0
[  201.093823]  ? vm_mmap_pgoff+0x117/0x1a0
[  201.097755]  ? srso_return_thunk+0x5/0x5f
[  201.101776]  ? srso_return_thunk+0x5/0x5f
[  201.105795]  ? syscall_exit_to_user_mode+0x78/0x200
[  201.110685]  ? srso_return_thunk+0x5/0x5f
[  201.114706]  ? do_syscall_64+0x87/0x160
[  201.118557]  ? srso_return_thunk+0x5/0x5f
[  201.122575]  ? __count_memcg_events+0x49/0xb0
[  201.126944]  ? srso_return_thunk+0x5/0x5f
[  201.130967]  ? srso_return_thunk+0x5/0x5f
[  201.134986]  ? syscall_exit_work+0xff/0x130
[  201.139184]  ? srso_return_thunk+0x5/0x5f
[  201.143205]  ? syscall_exit_to_user_mode+0x78/0x200
[  201.148093]  ? srso_return_thunk+0x5/0x5f
[  201.152114]  ? do_syscall_64+0x87/0x160
[  201.155960]  ? srso_return_thunk+0x5/0x5f
[  201.159984]  ? sched_clock_cpu+0xb/0x190
[  201.163916]  ? srso_return_thunk+0x5/0x5f
[  201.167939]  ? irqtime_account_irq+0x40/0xc0
[  201.172220]  ? srso_return_thunk+0x5/0x5f
[  201.176243]  ? srso_return_thunk+0x5/0x5f
[  201.180263]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
[  201.185326] RIP: 0033:0x7f26dfd0735b
[  201.188939] Code: Unable to access opcode bytes at 0x7f26dfd07331.
[  201.195128] RSP: 002b:00007fffce176868 EFLAGS: 00000206 ORIG_RAX: 000000000000000a
[  201.202700] RAX: fffffffffffffffc RBX: 00007f26dfe60000 RCX: 00007f26dfd0735b
[  201.209841] RDX: 0000000000000003 RSI: 0000000001000000 RDI: 00007f26af401000
[  201.216983] RBP: 00007f26b0400640 R08: 00000000ffffffff R09: 0000000000000000
[  201.224127] R10: ffffffffffffffc0 R11: 0000000000000206 R12: 0000000000000000
[  201.231267] R13: 000000000040d320 R14: 0000000000000000 R15: 0000000000000000
[  201.238413]  </TASK>
[  201.240610] ---[ end trace 0000000000000000 ]---
[  201.245250] unrecognized swap entry 0x7c00000000000001



> 
> Likely we want "Fixes:" here.

This could be seen as a continuation of the problem 
2ff559f31a5d Revert "userfaultfd: don't fail on unrecognized features" 
was trying to solve. However, this patch only checks to make sure we didnt 
ask for a feature outside the possible range of features. We are still missing
a check to confirm the requested features are also configured on. So I guess 
the "Fixes" tag would be for this patch?
914eedcb9ba0 userfaultfd: don't fail on unrecognized features

Happy to get your input here!

Thanks in advance!


> 
> > 
> > Signed-off-by: Audra Mitchell <audra@...hat.com>
> > ---
> >   fs/userfaultfd.c | 5 +++++
> >   1 file changed, 5 insertions(+)
> > 
> > diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> > index 60dcfafdc11a..17210558de79 100644
> > --- a/fs/userfaultfd.c
> > +++ b/fs/userfaultfd.c
> > @@ -2073,6 +2073,11 @@ static int userfaultfd_api(struct userfaultfd_ctx *ctx,
> >   	uffdio_api.features &= ~UFFD_FEATURE_WP_UNPOPULATED;
> >   	uffdio_api.features &= ~UFFD_FEATURE_WP_ASYNC;
> >   #endif
> > +
> > +	ret = -EINVAL;
> > +	if (features & ~uffdio_api.features)
> > +		goto err_out;
> > +
> >   	uffdio_api.ioctls = UFFD_API_IOCTLS;
> >   	ret = -EFAULT;
> >   	if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
> 
> CCing Peter.
> 
> -- 
> Cheers,
> 
> David / dhildenb
> 

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