From edfbc1285dd9ac624665fe9fa5de26437d61c1eb Mon Sep 17 00:00:00 2001 From: Alvin Chang Date: Thu, 3 Jul 2025 23:19:57 +0800 Subject: [PATCH] firmware: Initial compiler built-in stack protector support 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 Reviewed-by: Yu-Chien Peter Lin Reviewed-by: Anup Patel Link: https://lore.kernel.org/r/20250703151957.2545958-3-alvinga@andestech.com Signed-off-by: Anup Patel --- firmware/Kconfig | 27 +++++++++++++++++++++++++++ firmware/fw_base.S | 21 +++++++++++++++++++++ firmware/objects.mk | 9 +++++++++ firmware/payloads/test_head.S | 15 +++++++++++++++ 4 files changed, 72 insertions(+) diff --git a/firmware/Kconfig b/firmware/Kconfig index d6e0506a..c1fee190 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 2498797c..a008fa74 100644 --- a/firmware/fw_base.S +++ b/firmware/fw_base.S @@ -736,6 +736,27 @@ _reset_regs: ret + .section .rodata +.Lstack_corrupt_msg: + .string "stack smashing detected\n" + + /* 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: + la a0, .Lstack_corrupt_msg + call sbi_panic + + /* 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 a90485d0..bfec4671 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 7d25e07d..070ce8aa 100644 --- a/firmware/payloads/test_head.S +++ b/firmware/payloads/test_head.S @@ -97,3 +97,18 @@ _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 + .equ __stack_chk_fail, _start_hang + + /* 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