uprobes: Install_breakpoint() should fail if is_swbp_insn() == T

install_breakpoint() returns -EEXIST if is_swbp_insn(orig_insn)
== T, the caller treats this code as success.

This is doubly wrong. The successful return should set
UPROBE_COPY_INSN, but the real problem is that it shouldn't
succeed. If the probed insn is int3 the application should get
SIGTRAP, this won't happen with uprobe.

Probably we can fix this, we can add the UPROBE_SHARED_BP flag
and teach handle_swbp/set_orig_insn to handle this case
correctly. But this needs some complications and we have other
insns which can't be probed, lets make a simple fix for now.

I think this needs a cleanup. UPROBE_COPY_INSN should die,
copy_insn() should be called by alloc_uprobe().
arch_uprobe_analyze_insn() depends on ->mm (ia32_compat) but it
is called only once.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Anton Arapov <anton@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20120615154331.GA9578@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 3ccdb29ee8d6f4618b0229c267b26cc0762e145d..ec78152e32e9b04369c6a0108f911c54debc5b7d 100644 (file)
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -693,7 +693,7 @@ install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
                        return ret;
 
                if (is_swbp_insn((uprobe_opcode_t *)uprobe->arch.insn))
-                       return -EEXIST;
+                       return -ENOTSUPP;
 
                ret = arch_uprobe_analyze_insn(&uprobe->arch, mm, addr);
                if (ret)