[PATCH 4/4] ppc64 ftrace_with_regs recursion protection
From: Torsten Duwe <hidden>
Date: 2015-06-11 10:03:10
Also in:
lkml
Subsystem:
linux for powerpc (32-bit and 64-bit), the rest · Maintainers:
Madhavan Srinivasan, Michael Ellerman, Linus Torvalds
This is an *emergency* parachute to avoid an endless recursion and
consecutively a kernel stack overflow, should any function within some
ftrace framework cause an access fault, which calls _mcount / ftrace_caller
in return and so on. It might also call an ftrace'd function directly.
As Michael Ellerman pointed out, it is a tedious and error-prone task
to maintain a complete list of those functions that _might_ get called
from *_access_fault or any dynamic tracer function. So we'll
concentrate on the most frequent cases to enhance performance later,
while for now sticking with this fill-in. It will later serve as a backup
protection.
* arch/powerpc/kernel/entry_64.S:
- test-and-set TRACE_FTRACE_BIT in task_struct's trace_recursion,
do not call the actual tracer function if set, clear flag on return.
Signed-off-by: Torsten Duwe <redacted>
--
arch/powerpc/kernel/asm-offsets.c | 1 +
arch/powerpc/kernel/entry_64.S | 15 +++++++++++++--
2 files changed, 14 insertions(+), 2 deletions(-)
--diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index 4717859..ae10752 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c@@ -72,6 +72,7 @@ int main(void) DEFINE(THREAD, offsetof(struct task_struct, thread)); DEFINE(MM, offsetof(struct task_struct, mm)); DEFINE(MMCONTEXTID, offsetof(struct mm_struct, context.id)); + DEFINE(TASK_TRACEREC, offsetof(struct task_struct, trace_recursion)); #ifdef CONFIG_PPC64 DEFINE(AUDITCONTEXT, offsetof(struct task_struct, audit_context)); DEFINE(SIGSEGV, SIGSEGV);
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index a4132ef..4768104 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S@@ -1202,7 +1202,13 @@ _GLOBAL(ftrace_caller) SAVE_8GPRS(16,r1) SAVE_8GPRS(24,r1) - + ld r3, PACACURRENT(r13) + ld r4, TASK_TRACEREC(r3) + andi. r5, r4, 0x0010 // ( 1 << TRACE_FTRACE_BIT ) + ori r4, r4, 0x0010 + std r4, TASK_TRACEREC(r3) + bne- 3f // ftrace in progress - avoid recursion! + LOAD_REG_IMMEDIATE(r3,function_trace_op) ld r5,0(r3)
@@ -1224,9 +1230,14 @@ ftrace_call: bl ftrace_stub nop + ld r3, PACACURRENT(r13) + ld r4, TASK_TRACEREC(r3) + andi. r4, r4, 0xffef // ~( 1 << TRACE_FTRACE_BIT ) + std r4, TASK_TRACEREC(r3) + ld r3, _NIP(r1) mtlr r3 - +3: REST_8GPRS(0,r1) REST_8GPRS(8,r1) REST_8GPRS(16,r1)