From: madvenka@linux.microsoft.com
To: broonie@kernel.org, mark.rutland@arm.com, jpoimboe@redhat.com,
jthierry@redhat.com, catalin.marinas@arm.com, will@kernel.org,
linux-arm-kernel@lists.infradead.org,
live-patching@vger.kernel.org, linux-kernel@vger.kernel.org,
madvenka@linux.microsoft.com
Subject: [RFC PATCH v2 1/8] arm64: Implement stack trace termination record
Date: Mon, 15 Mar 2021 11:57:53 -0500 [thread overview]
Message-ID: <20210315165800.5948-2-madvenka@linux.microsoft.com> (raw)
In-Reply-To: <20210315165800.5948-1-madvenka@linux.microsoft.com>
From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>
The unwinder needs to be able to reliably tell when it has reached the end
of a stack trace. One way to do this is to have the last stack frame at a
fixed offset from the base of the task stack. When the unwinder reaches
that offset, it knows it is done.
Kernel Tasks
============
All tasks except the idle task have a pt_regs structure right after the
task stack. This is called the task pt_regs. The pt_regs structure has a
special stackframe field. Make this stackframe field the last frame in the
task stack. This needs to be done in copy_thread() which initializes a new
task's pt_regs and initial CPU context.
For the idle task, there is no task pt_regs. For our purpose, we need one.
So, create a pt_regs just like other kernel tasks and make
pt_regs->stackframe the last frame in the idle task stack. This needs to be
done at two places:
- On the primary CPU, the boot task runs. It calls start_kernel()
and eventually becomes the idle task for the primary CPU. Just
before start_kernel() is called, set up the last frame.
- On each secondary CPU, a startup task runs that calls
secondary_startup_kernel() and eventually becomes the idle task
on the secondary CPU. Just before secondary_start_kernel() is
called, set up the last frame.
User Tasks
==========
User tasks are initially set up like kernel tasks when they are created.
Then, they return to userland after fork via ret_from_fork(). After that,
they enter the kernel only on an EL0 exception. (In arm64, system calls are
also EL0 exceptions). The EL0 exception handler stores state in the task
pt_regs and calls different functions based on the type of exception. The
stack trace for an EL0 exception must end at the task pt_regs. So, make
task pt_regs->stackframe as the last frame in the EL0 exception stack.
In summary, task pt_regs->stackframe is where a successful stack trace ends.
Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
---
arch/arm64/kernel/entry.S | 8 +++++---
arch/arm64/kernel/head.S | 28 ++++++++++++++++++++++++----
arch/arm64/kernel/process.c | 5 +++++
3 files changed, 34 insertions(+), 7 deletions(-)
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index a31a0a713c85..e2dc2e998934 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -261,16 +261,18 @@ alternative_else_nop_endif
stp lr, x21, [sp, #S_LR]
/*
- * For exceptions from EL0, terminate the callchain here.
+ * For exceptions from EL0, terminate the callchain here at
+ * task_pt_regs(current)->stackframe.
+ *
* For exceptions from EL1, create a synthetic frame record so the
* interrupted code shows up in the backtrace.
*/
.if \el == 0
- mov x29, xzr
+ stp xzr, xzr, [sp, #S_STACKFRAME]
.else
stp x29, x22, [sp, #S_STACKFRAME]
- add x29, sp, #S_STACKFRAME
.endif
+ add x29, sp, #S_STACKFRAME
#ifdef CONFIG_ARM64_SW_TTBR0_PAN
alternative_if_not ARM64_HAS_PAN
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 66b0e0b66e31..2769b20934d4 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -393,6 +393,28 @@ SYM_FUNC_START_LOCAL(__create_page_tables)
ret x28
SYM_FUNC_END(__create_page_tables)
+ /*
+ * The boot task becomes the idle task for the primary CPU. The
+ * CPU startup task on each secondary CPU becomes the idle task
+ * for the secondary CPU.
+ *
+ * The idle task does not require pt_regs. But create a dummy
+ * pt_regs so that task_pt_regs(idle_task)->stackframe can be
+ * set up to be the last frame on the idle task stack just like
+ * all the other kernel tasks. This helps the unwinder to
+ * terminate the stack trace at a well-known stack offset.
+ *
+ * Also, set up the last return PC to be ret_from_fork() just
+ * like all the other kernel tasks so that the stack trace of
+ * all kernel tasks ends with the same function.
+ */
+ .macro setup_last_frame
+ sub sp, sp, #PT_REGS_SIZE
+ stp xzr, xzr, [sp, #S_STACKFRAME]
+ add x29, sp, #S_STACKFRAME
+ ldr x30, =ret_from_fork
+ .endm
+
/*
* The following fragment of code is executed with the MMU enabled.
*
@@ -447,8 +469,7 @@ SYM_FUNC_START_LOCAL(__primary_switched)
#endif
bl switch_to_vhe // Prefer VHE if possible
add sp, sp, #16
- mov x29, #0
- mov x30, #0
+ setup_last_frame
b start_kernel
SYM_FUNC_END(__primary_switched)
@@ -606,8 +627,7 @@ SYM_FUNC_START_LOCAL(__secondary_switched)
cbz x2, __secondary_too_slow
msr sp_el0, x2
scs_load x2, x3
- mov x29, #0
- mov x30, #0
+ setup_last_frame
#ifdef CONFIG_ARM64_PTR_AUTH
ptrauth_keys_init_cpu x2, x3, x4, x5
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 325c83b1a24d..7ffa689e8b60 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -437,6 +437,11 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start,
}
p->thread.cpu_context.pc = (unsigned long)ret_from_fork;
p->thread.cpu_context.sp = (unsigned long)childregs;
+ /*
+ * For the benefit of the unwinder, set up childregs->stackframe
+ * as the last frame for the new task.
+ */
+ p->thread.cpu_context.fp = (unsigned long)childregs->stackframe;
ptrace_hw_copy_thread(p);
--
2.25.1
next prev parent reply other threads:[~2021-03-15 16:59 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <5997dfe8d261a3a543667b83c902883c1e4bd270>
2021-03-15 16:57 ` [RFC PATCH v2 0/8] arm64: Implement reliable stack trace madvenka
2021-03-15 16:57 ` madvenka [this message]
2021-03-18 15:09 ` [RFC PATCH v2 1/8] arm64: Implement stack trace termination record Mark Brown
2021-03-18 20:26 ` Madhavan T. Venkataraman
2021-03-19 12:30 ` Mark Brown
2021-03-19 14:29 ` Madhavan T. Venkataraman
2021-03-19 18:19 ` Madhavan T. Venkataraman
2021-03-19 22:03 ` Madhavan T. Venkataraman
2021-03-23 10:24 ` Mark Rutland
2021-03-23 12:39 ` Madhavan T. Venkataraman
2021-03-15 16:57 ` [RFC PATCH v2 2/8] arm64: Implement frame types madvenka
2021-03-18 17:40 ` Mark Brown
2021-03-18 22:22 ` Madhavan T. Venkataraman
2021-03-19 13:22 ` Mark Brown
2021-03-19 14:40 ` Madhavan T. Venkataraman
2021-03-19 15:02 ` Madhavan T. Venkataraman
2021-03-19 16:20 ` Mark Brown
2021-03-19 16:27 ` Madhavan T. Venkataraman
2021-03-23 10:34 ` Mark Rutland
2021-03-15 16:57 ` [RFC PATCH v2 3/8] arm64: Terminate the stack trace at TASK_FRAME and EL0_FRAME madvenka
2021-03-18 18:26 ` Mark Brown
2021-03-18 20:29 ` Madhavan T. Venkataraman
2021-03-23 10:36 ` Mark Rutland
2021-03-23 12:40 ` Madhavan T. Venkataraman
2021-03-15 16:57 ` [RFC PATCH v2 4/8] arm64: Detect an EL1 exception frame and mark a stack trace unreliable madvenka
2021-03-23 10:42 ` Mark Rutland
2021-03-23 12:46 ` Madhavan T. Venkataraman
2021-03-23 13:04 ` Mark Rutland
2021-03-23 13:31 ` Madhavan T. Venkataraman
2021-03-23 14:33 ` Mark Rutland
2021-03-23 15:22 ` Madhavan T. Venkataraman
2021-03-15 16:57 ` [RFC PATCH v2 5/8] arm64: Detect an FTRACE " madvenka
2021-03-23 10:51 ` Mark Rutland
2021-03-23 12:56 ` Madhavan T. Venkataraman
2021-03-23 13:36 ` Mark Rutland
2021-03-23 13:38 ` Madhavan T. Venkataraman
2021-03-23 14:15 ` Madhavan T. Venkataraman
2021-03-23 14:57 ` Mark Rutland
2021-03-23 15:26 ` Madhavan T. Venkataraman
2021-03-23 16:20 ` Madhavan T. Venkataraman
2021-03-23 17:02 ` Mark Rutland
2021-03-23 17:23 ` Madhavan T. Venkataraman
2021-03-23 17:27 ` Madhavan T. Venkataraman
2021-03-23 18:27 ` Mark Brown
2021-03-23 20:23 ` Madhavan T. Venkataraman
2021-03-23 18:30 ` Mark Rutland
2021-03-23 20:24 ` Madhavan T. Venkataraman
2021-03-23 21:04 ` Madhavan T. Venkataraman
2021-03-23 16:48 ` Mark Rutland
2021-03-23 16:53 ` Madhavan T. Venkataraman
2021-03-23 17:09 ` Mark Rutland
2021-03-15 16:57 ` [RFC PATCH v2 6/8] arm64: Check the return PC of every stack frame madvenka
2021-03-15 16:57 ` [RFC PATCH v2 7/8] arm64: Detect kretprobed functions in stack trace madvenka
2021-03-15 16:58 ` [RFC PATCH v2 8/8] arm64: Implement arch_stack_walk_reliable() madvenka
2021-03-15 19:01 ` [RFC PATCH v2 0/8] arm64: Implement reliable stack trace Madhavan T. Venkataraman
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