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gcc-plugins: arm-ssp: Prepare for THREAD_INFO_IN_TASK support

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We will be enabling THREAD_INFO_IN_TASK support for ARM, which means
that we can no longer load the stack canary value by masking the stack
pointer and taking the copy that lives in thread_info. Instead, we will
be able to load it from the task_struct directly, by using the TPIDRURO
register which will hold the current task pointer when
THREAD_INFO_IN_TASK is in effect. This is much more straight-forward,
and allows us to declutter this code a bit while at it.

Note that this means that ARMv6 (non-v6K) SMP systems can no longer use
this feature, but those are quite rare to begin with, so this is a
reasonable trade off.

Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
This commit is contained in:
Ard Biesheuvel 2021-09-18 10:44:34 +02:00
parent 6880fa6c56
commit dfbdcda280
7 changed files with 8 additions and 39 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/arm/Kconfig
View File

@ -1600,7 +1600,7 @@ config XEN
config STACKPROTECTOR_PER_TASK
bool "Use a unique stack canary value for each task"
depends on GCC_PLUGINS && STACKPROTECTOR && SMP && !XIP_DEFLATED_DATA
depends on GCC_PLUGINS && STACKPROTECTOR && THREAD_INFO_IN_TASK && !XIP_DEFLATED_DATA
select GCC_PLUGIN_ARM_SSP_PER_TASK
default y
help

5
arch/arm/Makefile
View File

@ -273,11 +273,8 @@ ifeq ($(CONFIG_STACKPROTECTOR_PER_TASK),y)
prepare: stack_protector_prepare
stack_protector_prepare: prepare0
$(eval SSP_PLUGIN_CFLAGS := \
-fplugin-arg-arm_ssp_per_task_plugin-tso=$(shell \
awk '{if ($$2 == "THREAD_SZ_ORDER") print $$3;}'\
include/generated/asm-offsets.h) \
-fplugin-arg-arm_ssp_per_task_plugin-offset=$(shell \
awk '{if ($$2 == "TI_STACK_CANARY") print $$3;}'\
awk '{if ($$2 == "TSK_STACK_CANARY") print $$3;}'\
include/generated/asm-offsets.h))
$(eval KBUILD_CFLAGS += $(SSP_PLUGIN_CFLAGS))
$(eval GCC_PLUGINS_CFLAGS += $(SSP_PLUGIN_CFLAGS))

2
arch/arm/include/asm/stackprotector.h
View File

@ -39,8 +39,6 @@ static __always_inline void boot_init_stack_canary(void)
current->stack_canary = canary;
#ifndef CONFIG_STACKPROTECTOR_PER_TASK
__stack_chk_guard = current->stack_canary;
#else
current_thread_info()->stack_canary = current->stack_canary;
#endif
}

3
arch/arm/include/asm/thread_info.h
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@ -55,9 +55,6 @@ struct thread_info {
struct task_struct *task; /* main task structure */
__u32 cpu; /* cpu */
__u32 cpu_domain; /* cpu domain */
#ifdef CONFIG_STACKPROTECTOR_PER_TASK
unsigned long stack_canary;
#endif
struct cpu_context_save cpu_context; /* cpu context */
__u32 abi_syscall; /* ABI type and syscall nr */
__u8 used_cp[16]; /* thread used copro */

4
arch/arm/kernel/asm-offsets.c
View File

@ -63,10 +63,6 @@ int main(void)
#ifdef CONFIG_IWMMXT
DEFINE(TI_IWMMXT_STATE, offsetof(struct thread_info, fpstate.iwmmxt));
#endif
#ifdef CONFIG_STACKPROTECTOR_PER_TASK
DEFINE(TI_STACK_CANARY, offsetof(struct thread_info, stack_canary));
#endif
DEFINE(THREAD_SZ_ORDER, THREAD_SIZE_ORDER);
BLANK();
DEFINE(S_R0, offsetof(struct pt_regs, ARM_r0));
DEFINE(S_R1, offsetof(struct pt_regs, ARM_r1));

4
arch/arm/kernel/process.c
View File

@ -269,10 +269,6 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start,
thread_notify(THREAD_NOTIFY_COPY, thread);
#ifdef CONFIG_STACKPROTECTOR_PER_TASK
thread->stack_canary = p->stack_canary;
#endif
return 0;
}

27
scripts/gcc-plugins/arm_ssp_per_task_plugin.c
View File

@ -4,7 +4,7 @@
__visible int plugin_is_GPL_compatible;
static unsigned int sp_mask, canary_offset;
static unsigned int canary_offset;
static unsigned int arm_pertask_ssp_rtl_execute(void)
{
@ -13,7 +13,7 @@ static unsigned int arm_pertask_ssp_rtl_execute(void)
for (insn = get_insns(); insn; insn = NEXT_INSN(insn)) {
const char *sym;
rtx body;
rtx mask, masked_sp;
rtx current;
/*
* Find a SET insn involving a SYMBOL_REF to __stack_chk_guard
@ -30,19 +30,13 @@ static unsigned int arm_pertask_ssp_rtl_execute(void)
/*
* Replace the source of the SET insn with an expression that
* produces the address of the copy of the stack canary value
* stored in struct thread_info
* produces the address of the current task's stack canary value
*/
mask = GEN_INT(sext_hwi(sp_mask, GET_MODE_PRECISION(Pmode)));
masked_sp = gen_reg_rtx(Pmode);
current = gen_reg_rtx(Pmode);
emit_insn_before(gen_rtx_set(masked_sp,
gen_rtx_AND(Pmode,
stack_pointer_rtx,
mask)),
insn);
emit_insn_before(gen_load_tp_hard(current), insn);
SET_SRC(body) = gen_rtx_PLUS(Pmode, masked_sp,
SET_SRC(body) = gen_rtx_PLUS(Pmode, current,
GEN_INT(canary_offset));
}
return 0;
@ -72,7 +66,6 @@ __visible int plugin_init(struct plugin_name_args *plugin_info,
const char * const plugin_name = plugin_info->base_name;
const int argc = plugin_info->argc;
const struct plugin_argument *argv = plugin_info->argv;
int tso = 0;
int i;
if (!plugin_default_version_check(version, &gcc_version)) {
@ -91,11 +84,6 @@ __visible int plugin_init(struct plugin_name_args *plugin_info,
return 1;
}
if (!strcmp(argv[i].key, "tso")) {
tso = atoi(argv[i].value);
continue;
}
if (!strcmp(argv[i].key, "offset")) {
canary_offset = atoi(argv[i].value);
continue;
@ -105,9 +93,6 @@ __visible int plugin_init(struct plugin_name_args *plugin_info,
return 1;
}
/* create the mask that produces the base of the stack */
sp_mask = ~((1U << (12 + tso)) - 1);
PASS_INFO(arm_pertask_ssp_rtl, "expand", 1, PASS_POS_INSERT_AFTER);
register_callback(plugin_info->base_name, PLUGIN_PASS_MANAGER_SETUP,