tracing: Do not allow mmap() of persistent ring buffer

In the Linux kernel, the following vulnerability has been resolved:

tracing: Do not allow mmap() of persistent ring buffer

When trying to mmap a trace instance buffer that is attached to

reserve_mem, it would crash:

BUG: unable to handle page fault for address: ffffe97bd00025c8

#PF: supervisor read access in kernel mode

#PF: error_code(0x0000) - not-present page

PGD 2862f3067 P4D 2862f3067 PUD 0

Oops: Oops: 0000 [#1] PREEMPT_RT SMP PTI

CPU: 4 UID: 0 PID: 981 Comm: mmap-rb Not tainted 6.14.0-rc2-test-00003-g7f1a5e3fbf9e-dirty #233

Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014

RIP: 0010:validate_page_before_insert+0x5/0xb0

Code: e2 01 89 d0 c3 cc cc cc cc 66 66 2e 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1f 44 00 00 <48> 8b 46 08 a8 01 75 67 66 90 48 89 f0 8b 50 34 85 d2 74 76 48 89

RSP: 0018:ffffb148c2f3f968 EFLAGS: 00010246

RAX: ffff9fa5d3322000 RBX: ffff9fa5ccff9c08 RCX: 00000000b879ed29

RDX: ffffe97bd00025c0 RSI: ffffe97bd00025c0 RDI: ffff9fa5ccff9c08

RBP: ffffb148c2f3f9f0 R08: 0000000000000004 R09: 0000000000000004

R10: 0000000000000000 R11: 0000000000000200 R12: 0000000000000000

R13: 00007f16a18d5000 R14: ffff9fa5c48db6a8 R15: 0000000000000000

FS: 00007f16a1b54740(0000) GS:ffff9fa73df00000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: ffffe97bd00025c8 CR3: 00000001048c6006 CR4: 0000000000172ef0

Call Trace:

<TASK>

? __die_body.cold+0x19/0x1f

? __die+0x2e/0x40

? page_fault_oops+0x157/0x2b0

? search_module_extables+0x53/0x80

? validate_page_before_insert+0x5/0xb0

? kernelmode_fixup_or_oops.isra.0+0x5f/0x70

? __bad_area_nosemaphore+0x16e/0x1b0

? bad_area_nosemaphore+0x16/0x20

? do_kern_addr_fault+0x77/0x90

? exc_page_fault+0x22b/0x230

? asm_exc_page_fault+0x2b/0x30

? validate_page_before_insert+0x5/0xb0

? vm_insert_pages+0x151/0x400

__rb_map_vma+0x21f/0x3f0

ring_buffer_map+0x21b/0x2f0

tracing_buffers_mmap+0x70/0xd0

__mmap_region+0x6f0/0xbd0

mmap_region+0x7f/0x130

do_mmap+0x475/0x610

vm_mmap_pgoff+0xf2/0x1d0

ksys_mmap_pgoff+0x166/0x200

__x64_sys_mmap+0x37/0x50

x64_sys_call+0x1670/0x1d70

do_syscall_64+0xbb/0x1d0

entry_SYSCALL_64_after_hwframe+0x77/0x7f

The reason was that the code that maps the ring buffer pages to user space

has:

page = virt_to_page((void *)cpu_buffer->subbuf_ids[s]);

And uses that in:

vm_insert_pages(vma, vma->vm_start, pages, &nr_pages);

But virt_to_page() does not work with vmap()'d memory which is what the

persistent ring buffer has. It is rather trivial to allow this, but for

now just disable mmap() of instances that have their ring buffer from the

reserve_mem option.

If an mmap() is performed on a persistent buffer it will return -ENODEV

just like it would if the .mmap field wasn't defined in the

file_operations structure.