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  1. 23 Jul, 2020 1 commit
  3. 17 Jul, 2020 2 commits
  5. 16 Jul, 2020 8 commits
    • Will Deacon's avatar
      arm64: Use test_tsk_thread_flag() for checking TIF_SINGLESTEP · 5afc7855
      Will Deacon authored 
      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: default avatarWill Deacon <will@kernel.org>
      5afc7855
    • Will Deacon's avatar
      arm64: ptrace: Use NO_SYSCALL instead of -1 in syscall_trace_enter() · d83ee6e3
      Will Deacon authored 
      Setting a system call number of -1 is special, as it indicates that the
current system call should be skipped.

Use NO_SYSCALL instead of -1 when checking for this scenario, which is
different from the -1 returned due to a seccomp failure.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Keno Fischer <keno@juliacomputing.com>
Cc: Luis Machado <luis.machado@linaro.org>
Signed-off-by: default avatarWill Deacon <will@kernel.org>
      d83ee6e3
    • Will Deacon's avatar
      arm64: syscall: Expand the comment about ptrace and syscall(-1) · 139dbe5d
      Will Deacon authored 
      If a task executes syscall(-1), we intercept this early and force x0 to
be -ENOSYS so that we don't need to distinguish this scenario from one
where the scno is -1 because a tracer wants to skip the system call
using ptrace. With the return value set, the return path is the same as
the skip case.

Although there is a one-line comment noting this in el0_svc_common(), it
misses out most of the detail. Expand the comment to describe a bit more
about what is going on.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Keno Fischer <keno@juliacomputing.com>
Cc: Luis Machado <luis.machado@linaro.org>
Signed-off-by: default avatarWill Deacon <will@kernel.org>
      139dbe5d
    • Will Deacon's avatar
      arm64: ptrace: Add a comment describing our syscall entry/exit trap ABI · 59ee987e
      Will Deacon authored 
      Our tracehook logic for syscall entry/exit raises a SIGTRAP back to the
tracer following a ptrace request such as PTRACE_SYSCALL. As part of this
procedure, we clobber the reported value of one of the tracee's general
purpose registers (x7 for native tasks, r12 for compat) to indicate
whether the stop occurred on syscall entry or exit. This is a slightly
unfortunate ABI, as it prevents the tracer from accessing the real
register value and is at odds with other similar stops such as seccomp
traps.

Since we're stuck with this ABI, expand the comment in our tracehook
logic to acknowledge the issue and describe the behaviour in more detail.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Luis Machado <luis.machado@linaro.org>
Reported-by: default avatarKeno Fischer <keno@juliacomputing.com>
Signed-off-by: default avatarWill Deacon <will@kernel.org>
      59ee987e
    • Will Deacon's avatar
      arm64: compat: Ensure upper 32 bits of x0 are zero on syscall return · 15956689
      Will Deacon authored 
      Although we zero the upper bits of x0 on entry to the kernel from an
AArch32 task, we do not clear them on the exception return path and can
therefore expose 64-bit sign extended syscall return values to userspace
via interfaces such as the 'perf_regs' ABI, which deal exclusively with
64-bit registers.

Explicitly clear the upper 32 bits of x0 on return from a compat system
call.

Cc: <stable@vger.kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Keno Fischer <keno@juliacomputing.com>
Cc: Luis Machado <luis.machado@linaro.org>
Signed-off-by: default avatarWill Deacon <will@kernel.org>
      15956689
    • Will Deacon's avatar
      arm64: ptrace: Override SPSR.SS when single-stepping is enabled · 3a5a4366
      Will Deacon authored 
      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: <stable@vger.kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Keno Fischer <keno@juliacomputing.com>
Link: https://lore.kernel.org/r/1eed6d69-d53d-9657-1fc9-c089be07f98c@linaro.orgReported-by: default avatarLuis Machado <luis.machado@linaro.org>
Tested-by: default avatarLuis Machado <luis.machado@linaro.org>
Signed-off-by: default avatarWill Deacon <will@kernel.org>
      3a5a4366
    • Will Deacon's avatar
      arm64: ptrace: Consistently use pseudo-singlestep exceptions · ac2081cd
      Will Deacon authored 
      Although the arm64 single-step state machine can be fast-forwarded in
cases where we wish to generate a SIGTRAP without actually executing an
instruction, this has two major limitations outside of simply skipping
an instruction due to emulation.

1. Stepping out of a ptrace signal stop into a signal handler where
   SIGTRAP is blocked. Fast-forwarding the stepping state machine in
   this case will result in a forced SIGTRAP, with the handler reset to
   SIG_DFL.

2. The hardware implicitly fast-forwards the state machine when executing
   an SVC instruction for issuing a system call. This can interact badly
   with subsequent ptrace stops signalled during the execution of the
   system call (e.g. SYSCALL_EXIT or seccomp traps), as they may corrupt
   the stepping state by updating the PSTATE for the tracee.

Resolve both of these issues by injecting a pseudo-singlestep exception
on entry to a signal handler and also on return to userspace following a
system call.

Cc: <stable@vger.kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Tested-by: default avatarLuis Machado <luis.machado@linaro.org>
Reported-by: default avatarKeno Fischer <keno@juliacomputing.com>
Signed-off-by: default avatarWill Deacon <will@kernel.org>
      ac2081cd
    • Qi Liu's avatar
      drivers/perf: Fix kernel panic when rmmod PMU modules during perf sampling · bdc5c744
      Qi Liu authored 
      When users try to remove PMU modules during perf sampling, kernel panic
will happen because the pmu->read() is a NULL pointer here.

INFO on HiSilicon hip08 platform as follow:
pc : hisi_uncore_pmu_event_update+0x30/0xa4 [hisi_uncore_pmu]
lr : hisi_uncore_pmu_read+0x20/0x2c [hisi_uncore_pmu]
sp : ffff800010103e90
x29: ffff800010103e90 x28: ffff0027db0c0e40
x27: ffffa29a76f129d8 x26: ffffa29a77ceb000
x25: ffffa29a773a5000 x24: ffffa29a77392000
x23: ffffddffe5943f08 x22: ffff002784285960
x21: ffff002784285800 x20: ffff0027d2e76c80
x19: ffff0027842859e0 x18: ffff80003498bcc8
x17: ffffa29a76afe910 x16: ffffa29a7583f530
x15: 16151a1512061a1e x14: 0000000000000000
x13: ffffa29a76f1e238 x12: 0000000000000001
x11: 0000000000000400 x10: 00000000000009f0
x9 : ffff8000107b3e70 x8 : ffff0027db0c1890
x7 : ffffa29a773a7000 x6 : 00000007f5131013
x5 : 00000007f5131013 x4 : 09f257d417c00000
x3 : 00000002187bd7ce x2 : ffffa29a38f0f0d8
x1 : ffffa29a38eae268 x0 : ffff0027d2e76c80
Call trace:
hisi_uncore_pmu_event_update+0x30/0xa4 [hisi_uncore_pmu]
hisi_uncore_pmu_read+0x20/0x2c [hisi_uncore_pmu]
__perf_event_read+0x1a0/0x1f8
flush_smp_call_function_queue+0xa0/0x160
generic_smp_call_function_single_interrupt+0x18/0x20
handle_IPI+0x31c/0x4dc
gic_handle_irq+0x2c8/0x310
el1_irq+0xcc/0x180
arch_cpu_idle+0x4c/0x20c
default_idle_call+0x20/0x30
do_idle+0x1b4/0x270
cpu_startup_entry+0x28/0x30
secondary_start_kernel+0x1a4/0x1fc

To solve the above issue, current module should be registered to kernel,
so that try_module_get() can be invoked when perf sampling starts. This
adds the reference counting of module and could prevent users from removing
modules during sampling.
Reported-by: default avatarHaifeng Wang <wang.wanghaifeng@huawei.com>
Signed-off-by: default avatarQi Liu <liuqi115@huawei.com>
Reviewed-by: default avatarJohn Garry <john.garry@huawei.com>
Link: https://lore.kernel.org/r/1594891165-8228-1-git-send-email-liuqi115@huawei.comSigned-off-by: default avatarWill Deacon <will@kernel.org>
      bdc5c744
  7. 13 Jul, 2020 1 commit
    • Will Deacon's avatar
      efi/libstub/arm64: Retain 2MB kernel Image alignment if !KASLR · 7c116db2
      Will Deacon authored 
      Since commit 82046702 ("efi/libstub/arm64: Replace 'preferred' offset
with alignment check"), loading a relocatable arm64 kernel at a physical
address which is not 2MB aligned and subsequently booting with EFI will
leave the Image in-place, relying on the kernel to relocate itself early
during boot. In conjunction with commit dd4bc607 ("arm64: warn on
incorrect placement of the kernel by the bootloader"), which enables
CONFIG_RELOCATABLE by default, this effectively means that entering an
arm64 kernel loaded at an alignment smaller than 2MB with EFI (e.g. using
QEMU) will result in silent relocation at runtime.

Unfortunately, this has a subtle but confusing affect for developers
trying to inspect the PC value during a crash and comparing it to the
symbol addresses in vmlinux using tools such as 'nm' or 'addr2line';
all text addresses will be displaced by a sub-2MB offset, resulting in
the wrong symbol being identified in many cases. Passing "nokaslr" on
the command line or disabling "CONFIG_RANDOMIZE_BASE" does not help,
since the EFI stub only copies the kernel Image to a 2MB boundary if it
is not relocatable.

Adjust the EFI stub for arm64 so that the minimum Image alignment is 2MB
unless KASLR is in use.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: David Brazdil <dbrazdil@google.com>
Acked-by: default avatarArd Biesheuvel <ardb@kernel.org>
Signed-off-by: default avatarWill Deacon <will@kernel.org>
      7c116db2
  9. 09 Jul, 2020 2 commits
  11. 08 Jul, 2020 11 commits
  13. 03 Jul, 2020 3 commits
  15. 02 Jul, 2020 1 commit
    • Ard Biesheuvel's avatar
      arm64/alternatives: use subsections for replacement sequences · f7b93d42
      Ard Biesheuvel authored 
      When building very large kernels, the logic that emits replacement
sequences for alternatives fails when relative branches are present
in the code that is emitted into the .altinstr_replacement section
and patched in at the original site and fixed up. The reason is that
the linker will insert veneers if relative branches go out of range,
and due to the relative distance of the .altinstr_replacement from
the .text section where its branch targets usually live, veneers
may be emitted at the end of the .altinstr_replacement section, with
the relative branches in the sequence pointed at the veneers instead
of the actual target.

The alternatives patching logic will attempt to fix up the branch to
point to its original target, which will be the veneer in this case,
but given that the patch site is likely to be far away as well, it
will be out of range and so patching will fail. There are other cases
where these veneers are problematic, e.g., when the target of the
branch is in .text while the patch site is in .init.text, in which
case putting the replacement sequence inside .text may not help either.

So let's use subsections to emit the replacement code as closely as
possible to the patch site, to ensure that veneers are only likely to
be emitted if they are required at the patch site as well, in which
case they will be in range for the replacement sequence both before
and after it is transported to the patch site.

This will prevent alternative sequences in non-init code from being
released from memory after boot, but this is tolerable given that the
entire section is only 512 KB on an allyesconfig build (which weighs in
at 500+ MB for the entire Image). Also, note that modules today carry
the replacement sequences in non-init sections as well, and any of
those that target init code will be emitted into init sections after
this change.

This fixes an early crash when booting an allyesconfig kernel on a
system where any of the alternatives sequences containing relative
branches are activated at boot (e.g., ARM64_HAS_PAN on TX2)
Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Andre Przywara <andre.przywara@arm.com>
Cc: Dave P Martin <dave.martin@arm.com>
Link: https://lore.kernel.org/r/20200630081921.13443-1-ardb@kernel.orgSigned-off-by: default avatarWill Deacon <will@kernel.org>
      f7b93d42
  17. 25 Jun, 2020 2 commits
  19. 24 Jun, 2020 5 commits
  21. 23 Jun, 2020 4 commits
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