[PATCH] Make PTRACE_SINGLESTEP work with user helpers When userland jumps to kernel provided user helper page to perform operations like __kernel_cmpxchg trace_set_bpt() is unable to add breakpoints. Since single stepping is implemented with breakpoints this means that a process can effectively escape tracing completely. This patch treats jumps to user helper page as instructions that branch to LR since all user helpers return to LR.

[Timo Juhani Lindfors]

---
 arch/arm/kernel/ptrace.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c
index 3f562a7..5877c0e 100644
--- a/arch/arm/kernel/ptrace.c
+++ b/arch/arm/kernel/ptrace.c
@@ -26,6 +26,7 @@
 
 #include "ptrace.h"
 
+#define REG_LR	14
 #define REG_PC	15
 #define REG_PSR	16
 /*
@@ -329,6 +330,9 @@ get_branch_address(struct task_struct *child, unsigned long pc, unsigned long in
 	    break;
 	}
 
+	if (alt >= (void*)CONFIG_VECTORS_BASE && alt < (void*)CONFIG_VECTORS_BASE + PAGE_SIZE)
+		alt = get_user_reg(child, REG_LR);
+
 	return alt;
 }
 
-- 
1.5.6.5


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