[PATCH RESEND v4] riscv: Enable per-task stack canaries
From: guoren
Date: Thu Dec 17 2020 - 11:31:11 EST
From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
This enables the use of per-task stack canary values if GCC has
support for emitting the stack canary reference relative to the
value of tp, which holds the task struct pointer in the riscv
kernel.
After compare arm64 and x86 implementations, seems arm64's is more
flexible and readable. The key point is how gcc get the offset of
stack_canary from gs/el0_sp.
x86: Use a fix offset from gs, not flexible.
struct fixed_percpu_data {
/*
* GCC hardcodes the stack canary as %gs:40. Since the
* irq_stack is the object at %gs:0, we reserve the bottom
* 48 bytes of the irq stack for the canary.
*/
char gs_base[40]; // :(
unsigned long stack_canary;
};
arm64: Use -mstack-protector-guard-offset & guard-reg
gcc options:
-mstack-protector-guard=sysreg
-mstack-protector-guard-reg=sp_el0
-mstack-protector-guard-offset=xxx
riscv: Use -mstack-protector-guard-offset & guard-reg
gcc options:
-mstack-protector-guard=tls
-mstack-protector-guard-reg=tp
-mstack-protector-guard-offset=xxx
GCC's implementation has been merged:
commit c931e8d5a96463427040b0d11f9c4352ac22b2b0
Author: Cooper Qu <cooper.qu@xxxxxxxxxxxxxxxxx>
Date: Mon Jul 13 16:15:08 2020 +0800
RISC-V: Add support for TLS stack protector canary access
In the end, these codes are inserted by gcc before return:
* 0xffffffe00020b396 <+120>: ld a5,1008(tp) # 0x3f0
* 0xffffffe00020b39a <+124>: xor a5,a5,a4
* 0xffffffe00020b39c <+126>: mv a0,s5
* 0xffffffe00020b39e <+128>: bnez a5,0xffffffe00020b61c <_do_fork+766>
0xffffffe00020b3a2 <+132>: ld ra,136(sp)
0xffffffe00020b3a4 <+134>: ld s0,128(sp)
0xffffffe00020b3a6 <+136>: ld s1,120(sp)
0xffffffe00020b3a8 <+138>: ld s2,112(sp)
0xffffffe00020b3aa <+140>: ld s3,104(sp)
0xffffffe00020b3ac <+142>: ld s4,96(sp)
0xffffffe00020b3ae <+144>: ld s5,88(sp)
0xffffffe00020b3b0 <+146>: ld s6,80(sp)
0xffffffe00020b3b2 <+148>: ld s7,72(sp)
0xffffffe00020b3b4 <+150>: addi sp,sp,144
0xffffffe00020b3b6 <+152>: ret
...
* 0xffffffe00020b61c <+766>: auipc ra,0x7f8
* 0xffffffe00020b620 <+770>: jalr -1764(ra) # 0xffffffe000a02f38 <__stack_chk_fail>
Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
Signed-off-by: Cooper Qu <cooper.qu@xxxxxxxxxxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Palmer Dabbelt <palmerdabbelt@xxxxxxxxxx>
---
arch/riscv/Kconfig | 7 +++++++
arch/riscv/Makefile | 10 ++++++++++
arch/riscv/include/asm/stackprotector.h | 3 ++-
arch/riscv/kernel/asm-offsets.c | 3 +++
arch/riscv/kernel/process.c | 2 +-
5 files changed, 23 insertions(+), 2 deletions(-)
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index a627ae2..3d9daee 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -420,6 +420,13 @@ config EFI
allow the kernel to be booted as an EFI application. This
is only useful on systems that have UEFI firmware.
+config CC_HAVE_STACKPROTECTOR_TLS
+ def_bool $(cc-option,-mstack-protector-guard=tls -mstack-protector-guard-reg=tp -mstack-protector-guard-offset=0)
+
+config STACKPROTECTOR_PER_TASK
+ def_bool y
+ depends on STACKPROTECTOR && CC_HAVE_STACKPROTECTOR_TLS
+
endmenu
config BUILTIN_DTB
diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index b6eb946..508de08 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -67,6 +67,16 @@ KBUILD_CFLAGS_MODULE += $(call cc-option,-mno-relax)
# architectures. It's faster to have GCC emit only aligned accesses.
KBUILD_CFLAGS += $(call cc-option,-mstrict-align)
+ifeq ($(CONFIG_STACKPROTECTOR_PER_TASK),y)
+prepare: stack_protector_prepare
+stack_protector_prepare: prepare0
+ $(eval KBUILD_CFLAGS += -mstack-protector-guard=tls \
+ -mstack-protector-guard-reg=tp \
+ -mstack-protector-guard-offset=$(shell \
+ awk '{if ($$2 == "TSK_STACK_CANARY") print $$3;}' \
+ include/generated/asm-offsets.h))
+endif
+
# arch specific predefines for sparse
CHECKFLAGS += -D__riscv -D__riscv_xlen=$(BITS)
diff --git a/arch/riscv/include/asm/stackprotector.h b/arch/riscv/include/asm/stackprotector.h
index 5962f88..09093af 100644
--- a/arch/riscv/include/asm/stackprotector.h
+++ b/arch/riscv/include/asm/stackprotector.h
@@ -24,6 +24,7 @@ static __always_inline void boot_init_stack_canary(void)
canary &= CANARY_MASK;
current->stack_canary = canary;
- __stack_chk_guard = current->stack_canary;
+ if (!IS_ENABLED(CONFIG_STACKPROTECTOR_PER_TASK))
+ __stack_chk_guard = current->stack_canary;
}
#endif /* _ASM_RISCV_STACKPROTECTOR_H */
diff --git a/arch/riscv/kernel/asm-offsets.c b/arch/riscv/kernel/asm-offsets.c
index db20344..877ff65 100644
--- a/arch/riscv/kernel/asm-offsets.c
+++ b/arch/riscv/kernel/asm-offsets.c
@@ -66,6 +66,9 @@ void asm_offsets(void)
OFFSET(TASK_THREAD_F30, task_struct, thread.fstate.f[30]);
OFFSET(TASK_THREAD_F31, task_struct, thread.fstate.f[31]);
OFFSET(TASK_THREAD_FCSR, task_struct, thread.fstate.fcsr);
+#ifdef CONFIG_STACKPROTECTOR
+ OFFSET(TSK_STACK_CANARY, task_struct, stack_canary);
+#endif
DEFINE(PT_SIZE, sizeof(struct pt_regs));
OFFSET(PT_EPC, pt_regs, epc);
diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
index dd5f985..f786b5f 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -24,7 +24,7 @@
register unsigned long gp_in_global __asm__("gp");
-#ifdef CONFIG_STACKPROTECTOR
+#if defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_STACKPROTECTOR_PER_TASK)
#include <linux/stackprotector.h>
unsigned long __stack_chk_guard __read_mostly;
EXPORT_SYMBOL(__stack_chk_guard);
--
2.7.4