perf/x86/lbr: Filter vsyscall addresses

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

perf/x86/lbr: Filter vsyscall addresses

We found that a panic can occur when a vsyscall is made while LBR sampling

is active. If the vsyscall is interrupted (NMI) for perf sampling, this

call sequence can occur (most recent at top):

__insn_get_emulate_prefix()

insn_get_emulate_prefix()

insn_get_prefixes()

insn_get_opcode()

decode_branch_type()

get_branch_type()

intel_pmu_lbr_filter()

intel_pmu_handle_irq()

perf_event_nmi_handler()

Within __insn_get_emulate_prefix() at frame 0, a macro is called:

peek_nbyte_next(insn_byte_t, insn, i)

Within this macro, this dereference occurs:

(insn)->next_byte

Inspecting registers at this point, the value of the next_byte field is the

address of the vsyscall made, for example the location of the vsyscall

version of gettimeofday() at 0xffffffffff600000. The access to an address

in the vsyscall region will trigger an oops due to an unhandled page fault.

To fix the bug, filtering for vsyscalls can be done when

determining the branch type. This patch will return

a "none" branch if a kernel address if found to lie in the

vsyscall region.