[PATCH v2 2/2] firmware: Initial compiler built-in stack protector support
Alvin Chang
alvinga at andestech.com
Tue Jun 24 20:16:13 PDT 2025
Add __stack_chk_fail() and __stack_chk_guard variable which are used by
compiler built-in stack protector.
This patch just try to support stack-protector so the value of the stack
guard variable is simply fixed for now. It could be improved by
deriving from a random number generator, such as Zkr extension or any
platform-specific random number sources.
Introduce three configurations for the stack protector:
1. CONFIG_STACK_PROTECTOR to enable the stack protector feature by
providing "-fstack-protector" compiler flag
2. CONFIG_STACK_PROTECTOR_STRONG to provide "-fstack-protector-strong"
3. CONFIG_STACK_PROTECTOR_ALL to provide "-fstack-protector-all"
Instead of fixing the compiler flag of stack-protector feature as
"-fstack-protector", we derive it from the introduced Kconfig
configurations. The compiler flag "stack-protector-cflags-y" is defined
as Makefile "immediately expanded variables" with ":=". Thus, the
stronger configuration of the stack protector can overwrite the
preceding one.
Signed-off-by: Alvin Chang <alvinga at andestech.com>
---
firmware/Kconfig | 27 +++++++++++++++++++++++++++
firmware/fw_base.S | 17 +++++++++++++++++
firmware/objects.mk | 9 +++++++++
firmware/payloads/test_head.S | 17 +++++++++++++++++
4 files changed, 70 insertions(+)
diff --git a/firmware/Kconfig b/firmware/Kconfig
index d6e0506..c1fee19 100644
--- a/firmware/Kconfig
+++ b/firmware/Kconfig
@@ -1 +1,28 @@
# SPDX-License-Identifier: BSD-2-Clause
+
+menu "Stack Protector Support"
+
+config STACK_PROTECTOR
+ bool "Stack Protector buffer overflow detection"
+ default n
+ help
+ This option turns on the "stack-protector" compiler feature.
+
+config STACK_PROTECTOR_STRONG
+ bool "Strong Stack Protector"
+ depends on STACK_PROTECTOR
+ default n
+ help
+ Turn on the "stack-protector" with "-fstack-protector-strong" option.
+ Like -fstack-protector but includes additional functions to be
+ protected.
+
+config STACK_PROTECTOR_ALL
+ bool "Almighty Stack Protector"
+ depends on STACK_PROTECTOR
+ default n
+ help
+ Turn on the "stack-protector" with "-fstack-protector-all" option.
+ Like -fstack-protector except that all functions are protected.
+
+endmenu
diff --git a/firmware/fw_base.S b/firmware/fw_base.S
index 2498797..9dc73d0 100644
--- a/firmware/fw_base.S
+++ b/firmware/fw_base.S
@@ -736,6 +736,23 @@ _reset_regs:
ret
+ /* This will be called when the stack corruption is detected */
+ .section .text
+ .align 3
+ .globl __stack_chk_fail
+ .type __stack_chk_fail, %function
+__stack_chk_fail:
+ wfi
+ j __stack_chk_fail
+
+ /* Initial value of the stack guard variable */
+ .section .data
+ .align 3
+ .globl __stack_chk_guard
+ .type __stack_chk_guard, %object
+__stack_chk_guard:
+ RISCV_PTR 0x95B5FF5A
+
#ifdef FW_FDT_PATH
.section .rodata
.align 4
diff --git a/firmware/objects.mk b/firmware/objects.mk
index a90485d..bfec467 100644
--- a/firmware/objects.mk
+++ b/firmware/objects.mk
@@ -66,3 +66,12 @@ endif
ifdef FW_OPTIONS
firmware-genflags-y += -DFW_OPTIONS=$(FW_OPTIONS)
endif
+
+ifeq ($(CONFIG_STACK_PROTECTOR),y)
+stack-protector-cflags-$(CONFIG_STACK_PROTECTOR) := -fstack-protector
+stack-protector-cflags-$(CONFIG_STACK_PROTECTOR_STRONG) := -fstack-protector-strong
+stack-protector-cflags-$(CONFIG_STACK_PROTECTOR_ALL) := -fstack-protector-all
+else
+stack-protector-cflags-y := -fno-stack-protector
+endif
+firmware-cflags-y += $(stack-protector-cflags-y)
diff --git a/firmware/payloads/test_head.S b/firmware/payloads/test_head.S
index 7d25e07..b5fd46b 100644
--- a/firmware/payloads/test_head.S
+++ b/firmware/payloads/test_head.S
@@ -97,3 +97,20 @@ _boot_a0:
RISCV_PTR 0
_boot_a1:
RISCV_PTR 0
+
+ /* This will be called when the stack corruption is detected */
+ .section .text
+ .align 3
+ .globl __stack_chk_fail
+ .type __stack_chk_fail, %function
+__stack_chk_fail:
+ wfi
+ j __stack_chk_fail
+
+ /* Initial value of the stack guard variable */
+ .section .data
+ .align 3
+ .globl __stack_chk_guard
+ .type __stack_chk_guard, %object
+__stack_chk_guard:
+ RISCV_PTR 0x95B5FF5A
--
2.43.0
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