linux.git/arch/arm64/kernel/debug-monitors.c, branch v5.10

arm64: Improve diagnostics when trapping BRK with FAULT_BRK_IMM

2020-09-18T15:35:54+00:00

When generating instructions at runtime, for example due to kernel text
patching or the BPF JIT, we can emit a trapping BRK instruction if we
are asked to encode an invalid instruction such as an out-of-range]
branch. This is indicative of a bug in the caller, and will result in a
crash on executing the generated code. Unfortunately, the message from
the crash is really unhelpful, and mumbles something about ptrace:

  | Unexpected kernel BRK exception at EL1
  | Internal error: ptrace BRK handler: f2000100 [#1] SMP

We can do better than this. Install a break handler for FAULT_BRK_IMM,
which is the immediate used to encode the "I've been asked to generate
an invalid instruction" error, and triage the faulting PC to determine
whether or not the failure occurred in the BPF JIT.

Link: https://lore.kernel.org/r/20200915141707.GB26439@willie-the-truck
Reported-by: Ilias Apalodimas 
Signed-off-by: Will Deacon

arm64: Use test_tsk_thread_flag() for checking TIF_SINGLESTEP

2020-07-16T10:42:12+00:00

Rather than open-code test_tsk_thread_flag() at each callsite, simply
replace the couple of offenders with calls to test_tsk_thread_flag()
directly.

Signed-off-by: Will Deacon

arm64: ptrace: Override SPSR.SS when single-stepping is enabled

2020-07-16T10:41:21+00:00

Luis reports that, when reverse debugging with GDB, single-step does not
function as expected on arm64:

  | I've noticed, under very specific conditions, that a PTRACE_SINGLESTEP
  | request by GDB won't execute the underlying instruction. As a consequence,
  | the PC doesn't move, but we return a SIGTRAP just like we would for a
  | regular successful PTRACE_SINGLESTEP request.

The underlying problem is that when the CPU register state is restored
as part of a reverse step, the SPSR.SS bit is cleared and so the hardware
single-step state can transition to the "active-pending" state, causing
an unexpected step exception to be taken immediately if a step operation
is attempted.

In hindsight, we probably shouldn't have exposed SPSR.SS in the pstate
accessible by the GPR regset, but it's a bit late for that now. Instead,
simply prevent userspace from configuring the bit to a value which is
inconsistent with the TIF_SINGLESTEP state for the task being traced.

Cc: 
Cc: Mark Rutland 
Cc: Keno Fischer 
Link: https://lore.kernel.org/r/1eed6d69-d53d-9657-1fc9-c089be07f98c@linaro.org
Reported-by: Luis Machado 
Tested-by: Luis Machado 
Signed-off-by: Will Deacon

arm64: debug: mark a function as __init to save some memory

2020-06-04T15:21:29+00:00

'debug_monitors_init()' is only called via 'postcore_initcall'.
It can be marked as __init to save a few bytes of memory.

Signed-off-by: Christophe JAILLET 
Reviewed-by: Douglas Anderson 
Link: https://lore.kernel.org/r/20200531110015.598607-1-christophe.jaillet@wanadoo.fr
Signed-off-by: Will Deacon

arm64: Call debug_traps_init() from trap_init() to help early kgdb

2020-05-18T16:51:20+00:00

A new kgdb feature will soon land (kgdb_earlycon) that lets us run
kgdb much earlier.  In order for everything to work properly it's
important that the break hook is setup by the time we process
"kgdbwait".

Right now the break hook is setup in debug_traps_init() and that's
called from arch_initcall().  That's a bit too late since
kgdb_earlycon really needs things to be setup by the time the system
calls dbg_late_init().

We could fix this by adding call_break_hook() into early_brk64() and
that works fine.  However, it's a little ugly.  Instead, let's just
add a call to debug_traps_init() straight from trap_init().  There's
already a documented dependency between trap_init() and
debug_traps_init() and this makes the dependency more obvious rather
than just relying on a comment.

NOTE: this solution isn't early enough to let us select the
"ARCH_HAS_EARLY_DEBUG" KConfig option that is introduced by the
kgdb_earlycon patch series.  That would only be set if we could do
breakpoints when early params are parsed.  This patch only enables
"late early" breakpoints, AKA breakpoints when dbg_late_init() is
called.  It's expected that this should be fine for most people.

It should also be noted that if you crash you can still end up in kgdb
earlier than debug_traps_init().  Since you don't need breakpoints to
debug a crash that's fine.

Suggested-by: Will Deacon 
Signed-off-by: Douglas Anderson 
Acked-by: Will Deacon 
Cc: Catalin Marinas 
Cc: Will Deacon 
Link: https://lore.kernel.org/r/20200513160501.1.I0b5edf030cc6ebef6ab4829f8867cdaea42485d8@changeid
Signed-off-by: Will Deacon

arm64: Remove unneeded rcu_read_lock from debug handlers

2019-08-01T14:00:27+00:00

Remove rcu_read_lock()/rcu_read_unlock() from debug exception
handlers since we are sure those are not preemptible and
interrupts are off.

Acked-by: Paul E. McKenney 
Signed-off-by: Masami Hiramatsu 
Signed-off-by: Will Deacon

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 234

2019-06-19T15:09:07+00:00

Based on 1 normalized pattern(s):

  this program is free software you can redistribute it and or modify
  it under the terms of the gnu general public license version 2 as
  published by the free software foundation this program is
  distributed in the hope that it will be useful but without any
  warranty without even the implied warranty of merchantability or
  fitness for a particular purpose see the gnu general public license
  for more details you should have received a copy of the gnu general
  public license along with this program if not see http www gnu org
  licenses

extracted by the scancode license scanner the SPDX license identifier

  GPL-2.0-only

has been chosen to replace the boilerplate/reference in 503 file(s).

Signed-off-by: Thomas Gleixner 
Reviewed-by: Alexios Zavras 
Reviewed-by: Allison Randal 
Reviewed-by: Enrico Weigelt 
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190602204653.811534538@linutronix.de
Signed-off-by: Greg Kroah-Hartman

arm64: Clear OSDLR_EL1 on CPU boot

2019-04-09T11:38:31+00:00

Some firmwares may reboot CPUs with OS Double Lock set. Make sure that
it is unlocked, in order to use debug exceptions.

Cc: 
Signed-off-by: Jean-Philippe Brucker 
Signed-off-by: Will Deacon

arm64: debug: Clean up brk_handler()

2019-04-09T10:21:13+00:00

brk_handler() now looks pretty strange and can be refactored to drop its
funny 'handler_found' local variable altogether.

Reviewed-by: Mark Rutland 
Signed-off-by: Will Deacon

arm64: probes: Move magic BRK values into brk-imm.h

2019-04-09T10:21:13+00:00

kprobes and uprobes reserve some BRK immediates for installing their
probes. Define these along with the other reservations in brk-imm.h
and rename the ESR definitions to be consistent with the others that we
already have.

Reviewed-by: Mark Rutland 
Signed-off-by: Will Deacon