linux_dsm_epyc7002/arch/arm64/kernel
Dave Martin 071b6d4a5d arm64: fpsimd: Prevent registers leaking from dead tasks
Currently, loading of a task's fpsimd state into the CPU registers
is skipped if that task's state is already present in the registers
of that CPU.

However, the code relies on the struct fpsimd_state * (and by
extension struct task_struct *) to unambiguously identify a task.

There is a particular case in which this doesn't work reliably:
when a task exits, its task_struct may be recycled to describe a
new task.

Consider the following scenario:

 1) Task P loads its fpsimd state onto cpu C.
        per_cpu(fpsimd_last_state, C) := P;
        P->thread.fpsimd_state.cpu := C;

 2) Task X is scheduled onto C and loads its fpsimd state on C.
        per_cpu(fpsimd_last_state, C) := X;
        X->thread.fpsimd_state.cpu := C;

 3) X exits, causing X's task_struct to be freed.

 4) P forks a new child T, which obtains X's recycled task_struct.
	T == X.
	T->thread.fpsimd_state.cpu == C (inherited from P).

 5) T is scheduled on C.
	T's fpsimd state is not loaded, because
	per_cpu(fpsimd_last_state, C) == T (== X) &&
	T->thread.fpsimd_state.cpu == C.

        (This is the check performed by fpsimd_thread_switch().)

So, T gets X's registers because the last registers loaded onto C
were those of X, in (2).

This patch fixes the problem by ensuring that the sched-in check
fails in (5): fpsimd_flush_task_state(T) is called when T is
forked, so that T->thread.fpsimd_state.cpu == C cannot be true.
This relies on the fact that T is not schedulable until after
copy_thread() completes.

Once T's fpsimd state has been loaded on some CPU C there may still
be other cpus D for which per_cpu(fpsimd_last_state, D) ==
&X->thread.fpsimd_state.  But D is necessarily != C in this case,
and the check in (5) must fail.

An alternative fix would be to do refcounting on task_struct.  This
would result in each CPU holding a reference to the last task whose
fpsimd state was loaded there.  It's not clear whether this is
preferable, and it involves higher overhead than the fix proposed
in this patch.  It would also move all the task_struct freeing
work into the context switch critical section, or otherwise some
deferred cleanup mechanism would need to be introduced, neither of
which seems obviously justified.

Cc: <stable@vger.kernel.org>
Fixes: 005f78cd88 ("arm64: defer reloading a task's FPSIMD state to userland resume")
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
[will: word-smithed the comment so it makes more sense]
Signed-off-by: Will Deacon <will.deacon@arm.com>
2017-12-06 18:02:21 +00:00
..
probes License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
vdso arm64 updates for 4.15 2017-11-15 10:56:56 -08:00
.gitignore arm64: Build infrastructure 2012-09-17 13:42:21 +01:00
acpi_numa.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
acpi_parking_protocol.c arm64: fix endianness annotation in acpi_parking_protocol.c 2017-06-29 11:33:15 +01:00
acpi.c ACPI / boot: Correct address space of __acpi_map_table() 2017-07-24 22:47:56 +02:00
alternative.c arm64: fix endianness annotation for __apply_alternatives()/get_alt_insn() 2017-06-29 16:32:43 +01:00
arm64ksyms.c arm64: switch to RAW_COPY_USER 2017-03-28 18:23:24 -04:00
armv8_deprecated.c arm64 updates for 4.15 2017-11-15 10:56:56 -08:00
asm-offsets.c arm64: unwind: reference pt_regs via embedded stack frame 2017-08-09 14:07:13 +01:00
cacheinfo.c arm64: cacheinfo: Remove CCSIDR-based cache information probing 2017-03-20 16:16:54 +00:00
cpu_errata.c arm64: Add workaround for Cavium Thunder erratum 30115 2017-06-15 09:45:04 +01:00
cpu_ops.c arm64: cpu_ops: Add missing 'const' qualifiers 2017-12-01 13:05:08 +00:00
cpu-reset.h arm64: Use __pa_symbol for kernel symbols 2017-01-12 15:05:39 +00:00
cpu-reset.S arm64: Add back cpu reset routines 2016-06-27 16:31:25 +01:00
cpufeature.c arm64 updates for 4.15 2017-11-15 10:56:56 -08:00
cpuidle.c arm64: kernel: Update kerneldoc for cpu_suspend() rename 2017-03-10 18:06:24 +00:00
cpuinfo.c arm64/sve: Detect SVE and activate runtime support 2017-11-03 15:24:21 +00:00
crash_dump.c arm64: kdump: provide /proc/vmcore file 2017-04-05 18:31:38 +01:00
debug-monitors.c arm64: introduce an order for exceptions 2017-11-02 15:55:41 +00:00
efi-entry.S arm64: efi-entry.S: avoid open-coded adr_l 2017-01-17 17:41:14 +00:00
efi-header.S arm64: efi: split Image code and data into separate PE/COFF sections 2017-04-04 17:50:59 +01:00
efi.c efi/arm: Enable DMI/SMBIOS 2017-06-05 17:50:44 +02:00
entry32.S arm64: entry32: remove pointless register assignment 2015-07-10 16:47:13 +01:00
entry-fpsimd.S arm64/sve: Low-level SVE architectural state manipulation functions 2017-11-03 15:24:14 +00:00
entry-ftrace.S arm64: Fix static use of function graph 2017-11-03 12:05:23 +00:00
entry.S arm64/sve: Detect SVE and activate runtime support 2017-11-03 15:24:21 +00:00
fpsimd.c arm64: fpsimd: Fix failure to restore FPSIMD state after signals 2017-12-01 13:05:05 +00:00
ftrace.c arm64: ftrace: emit ftrace-mod.o contents through code 2017-12-01 13:04:59 +00:00
head.S arm64/sve: Low-level CPU setup 2017-11-03 15:24:15 +00:00
hibernate-asm.S arm64: Introduce raw_{d,i}cache_line_size 2016-09-09 15:03:29 +01:00
hibernate.c arm64: explicitly mask all exceptions 2017-11-02 15:55:40 +00:00
hw_breakpoint.c arm64: hw_breakpoint: fix watchpoint matching for tagged pointers 2017-05-09 17:26:40 +01:00
hyp-stub.S arm64: hyp-stub: Zero x0 on successful stub handling 2017-04-09 07:49:35 -07:00
image.h arm64 updates for 4.7: 2016-05-16 17:17:24 -07:00
insn.c arm64 updates for 4.13: 2017-07-05 17:09:27 -07:00
io.c arm64: Avoid aligning normal memory pointers in __memcpy_{to,from}io 2017-10-24 16:23:07 +01:00
irq.c arm64: add basic VMAP_STACK support 2017-08-15 18:36:04 +01:00
jump_label.c jump_label: Rename JUMP_LABEL_{EN,DIS}ABLE to JUMP_LABEL_{JMP,NOP} 2015-08-03 11:34:12 +02:00
kaslr.c arm64: kaslr: Adjust the offset to avoid Image across alignment boundary 2017-08-22 18:15:42 +01:00
kgdb.c sched/headers: Prepare for new header dependencies before moving code to <linux/sched/task_stack.h> 2017-03-02 08:42:36 +01:00
kuser32.S arm64: Add __NR_* definitions for compat syscalls 2014-07-10 11:02:40 +01:00
machine_kexec.c arm64: explicitly mask all exceptions 2017-11-02 15:55:40 +00:00
Makefile arm64: ftrace: emit ftrace-mod.o contents through code 2017-12-01 13:04:59 +00:00
module-plts.c arm64: ftrace: emit ftrace-mod.o contents through code 2017-12-01 13:04:59 +00:00
module.c arm64: fix endianness annotation for reloc_insn_movw() & reloc_insn_imm() 2017-06-29 11:09:39 +01:00
module.lds arm64: ftrace: emit ftrace-mod.o contents through code 2017-12-01 13:04:59 +00:00
paravirt.c arm64: introduce CONFIG_PARAVIRT, PARAVIRT_TIME_ACCOUNTING and pv_time_ops 2015-12-21 14:40:54 +00:00
pci.c PCI: Add a generic weak pcibios_align_resource() 2017-08-02 14:53:16 -05:00
perf_callchain.c arm64: unwind: remove sp from struct stackframe 2017-08-09 14:10:29 +01:00
perf_event.c arm64: perf: remove unsupported events for Cortex-A73 2017-12-01 13:05:08 +00:00
perf_regs.c License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
process.c arm64: fpsimd: Prevent registers leaking from dead tasks 2017-12-06 18:02:21 +00:00
psci.c arm64: Use __pa_symbol for kernel symbols 2017-01-12 15:05:39 +00:00
ptrace.c arm64/sve: ptrace and ELF coredump support 2017-11-03 15:24:18 +00:00
reloc_test_core.c arm64: relocation testing module 2017-04-04 17:03:32 +01:00
reloc_test_syms.S arm64: relocation testing module 2017-04-04 17:03:32 +01:00
relocate_kernel.S arm64: Introduce raw_{d,i}cache_line_size 2016-09-09 15:03:29 +01:00
return_address.c arm64: unwind: remove sp from struct stackframe 2017-08-09 14:10:29 +01:00
setup.c arm64: Move the async/fiq helpers to explicitly set process context flags 2017-11-02 15:55:41 +00:00
signal32.c arm64/sve: Signal handling support 2017-11-03 15:24:16 +00:00
signal.c arm64/sve: Signal handling support 2017-11-03 15:24:16 +00:00
sleep.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
smccc-call.S firmware: qcom: scm: Fix interrupted SCM calls 2017-02-03 18:46:33 +00:00
smp_spin_table.c arm64: Use __pa_symbol for kernel symbols 2017-01-12 15:05:39 +00:00
smp.c arm64: Move the async/fiq helpers to explicitly set process context flags 2017-11-02 15:55:41 +00:00
stacktrace.c arm64: stacktrace: avoid listing stacktrace functions in stacktrace 2017-09-13 18:53:16 -07:00
suspend.c arm64 updates for 4.15 2017-11-15 10:56:56 -08:00
sys32.c arm64: fix implementation of mmap2 compat syscall 2015-03-19 10:43:51 +00:00
sys_compat.c sched/headers: Prepare for the reduction of <linux/sched.h>'s signal API dependency 2017-03-02 08:42:37 +01:00
sys.c arm64: compat: Check for AArch32 state 2016-04-20 12:22:42 +01:00
time.c arm64: unwind: remove sp from struct stackframe 2017-08-09 14:10:29 +01:00
topology.c arm64: Convert to using %pOF instead of full_name 2017-07-20 10:28:41 +01:00
trace-events-emulation.h License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
traps.c arm64 updates for 4.15 2017-11-15 10:56:56 -08:00
vdso.c arm64/vdso: Support mremap() for vDSO 2017-08-09 12:16:28 +01:00
vmlinux.lds.S License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00