Commit cdc27c27 authored Dec 17, 2013 by Will Deacon Committed by Catalin Marinas Dec 19, 2013

arm64: ptrace: avoid using HW_BREAKPOINT_EMPTY for disabled events



Commit 8f34a1da ("arm64: ptrace: use HW_BREAKPOINT_EMPTY type for
disabled breakpoints") fixed an issue with GDB trying to zero breakpoint
control registers. The problem there is that the arch hw_breakpoint code
will attempt to create a (disabled), execute breakpoint of length 0.

This will fail validation and report unexpected failure to GDB. To avoid
this, we treated disabled breakpoints as HW_BREAKPOINT_EMPTY, but that
seems to have broken with recent kernels, causing watchpoints to be
treated as TYPE_INST in the core code and returning ENOSPC for any
further breakpoints.

This patch fixes the problem by prioritising the `enable' field of the
breakpoint: if it is cleared, we simply update the perf_event_attr to
indicate that the thing is disabled and don't bother changing either the
type or the length. This reinforces the behaviour that the breakpoint
control register is essentially read-only apart from the enable bit
when disabling a breakpoint.

Cc: <stable@vger.kernel.org>
Reported-by: Aaron Liu <liucy214@gmail.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

parent 319e2e3f

arch/arm64/kernel/ptrace.c

+18 −20

Original line number	Diff line number	Diff line
		@@ -214,10 +214,10 @@ static int ptrace_hbp_fill_attr_ctrl(unsigned int note_type,
		{
		int err, len, type, disabled = !ctrl.enabled;

		if (disabled) {
		len = 0;
		type = HW_BREAKPOINT_EMPTY;
		} else {
		attr->disabled = disabled;
		if (disabled)
		return 0;

		err = arch_bp_generic_fields(ctrl, &len, &type);
		if (err)
		return err;
		@@ -234,11 +234,9 @@ static int ptrace_hbp_fill_attr_ctrl(unsigned int note_type,
		default:
		return -EINVAL;
		}
		}

		attr->bp_len = len;
		attr->bp_type = type;
		attr->disabled = disabled;

		return 0;
		}

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