On ARM, we currently only change the value of the stack canary when switching tasks if the kernel was built for UP. On SMP kernels, this is impossible since the stack canary value is obtained via a global symbol reference, which means a) all running tasks on all CPUs must use the same value b) we can only modify the value when no kernel stack frames are live on any CPU, which is effectively never. So instead, use a GCC plugin to add a RTL pass that replaces each reference to the address of the __stack_chk_guard symbol with an expression that produces the address of the 'stack_canary' field that is added to struct thread_info. This way, each task will use its own randomized value.
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| @@ -36,6 +36,12 @@ ifdef CONFIG_GCC_PLUGIN_STACKLEAK · 35 unmodified lines | ||
| 36 | 36 | endif |
| 37 | 37 | export DISABLE_STACKLEAK_PLUGIN |
| 38 | 38 | |
| 39 | +gcc-plugin-$(CONFIG_GCC_PLUGIN_ARM_SSP_PER_TASK) += arm_ssp_per_task_plugin.so | |
| 40 | +ifdef CONFIG_GCC_PLUGIN_ARM_SSP_PER_TASK | |
| 41 | + DISABLE_ARM_SSP_PER_TASK_PLUGIN += -fplugin-arg-arm_ssp_per_task_plugin-disable | |
| 42 | +endif | |
| 43 | +export DISABLE_ARM_SSP_PER_TASK_PLUGIN | |
| 44 | + | |
| 39 | 45 | # All the plugin CFLAGS are collected here in case a build target needs to |
| 40 | 46 | # filter them out of the KBUILD_CFLAGS. |
| 41 | 47 | GCC_PLUGINS_CFLAGS := $(strip $(addprefix -fplugin=$(objtree)/scripts/gcc-plugins/, $(gcc-plugin-y)) $(gcc-plugin-cflags-y)) |
| @@ -190,4 +190,8 @@ config STACKLEAK_RUNTIME_DISABLE · 189 unmodified lines | ||
| 190 | 190 | runtime to control kernel stack erasing for kernels built with |
| 191 | 191 | CONFIG_GCC_PLUGIN_STACKLEAK. |
| 192 | 192 | |
| 193 | +config GCC_PLUGIN_ARM_SSP_PER_TASK | |
| 194 | + bool | |
| 195 | + depends on GCC_PLUGINS && ARM | |
| 196 | + | |
| 193 | 197 | endif |
| @@ -0,0 +1,103 @@ | ||
| 1 | +// SPDX-License-Identifier: GPL-2.0 | |
| 2 | + | |
| 3 | +#include "gcc-common.h" | |
| 4 | + | |
| 5 | +__visible int plugin_is_GPL_compatible; | |
| 6 | + | |
| 7 | +static unsigned int sp_mask, canary_offset; | |
| 8 | + | |
| 9 | +static unsigned int arm_pertask_ssp_rtl_execute(void) | |
| 10 | +{ | |
| 11 | + rtx_insn *insn; | |
| 12 | + | |
| 13 | + for (insn = get_insns(); insn; insn = NEXT_INSN(insn)) { | |
| 14 | + const char *sym; | |
| 15 | + rtx body; | |
| 16 | + rtx masked_sp; | |
| 17 | + | |
| 18 | + /* | |
| 19 | + * Find a SET insn involving a SYMBOL_REF to __stack_chk_guard | |
| 20 | + */ | |
| 21 | + if (!INSN_P(insn)) | |
| 22 | + continue; | |
| 23 | + body = PATTERN(insn); | |
| 24 | + if (GET_CODE(body) != SET || | |
| 25 | + GET_CODE(SET_SRC(body)) != SYMBOL_REF) | |
| 26 | + continue; | |
| 27 | + sym = XSTR(SET_SRC(body), 0); | |
| 28 | + if (strcmp(sym, "__stack_chk_guard")) | |
| 29 | + continue; | |
| 30 | + | |
| 31 | + /* | |
| 32 | + * Replace the source of the SET insn with an expression that | |
| 33 | + * produces the address of the copy of the stack canary value | |
| 34 | + * stored in struct thread_info | |
| 35 | + */ | |
| 36 | + masked_sp = gen_reg_rtx(Pmode); | |
| 37 | + | |
| 38 | + emit_insn_before(gen_rtx_SET(masked_sp, | |
| 39 | + gen_rtx_AND(Pmode, | |
| 40 | + stack_pointer_rtx, | |
| 41 | + GEN_INT(sp_mask))), | |
| 42 | + insn); | |
| 43 | + | |
| 44 | + SET_SRC(body) = gen_rtx_PLUS(Pmode, masked_sp, | |
| 45 | + GEN_INT(canary_offset)); | |
| 46 | + } | |
| 47 | + return 0; | |
| 48 | +} | |
| 49 | + | |
| 50 | +#define PASS_NAME arm_pertask_ssp_rtl | |
| 51 | + | |
| 52 | +#define NO_GATE | |
| 53 | +#include "gcc-generate-rtl-pass.h" | |
| 54 | + | |
| 55 | +__visible int plugin_init(struct plugin_name_args *plugin_info, | |
| 56 | + struct plugin_gcc_version *version) | |
| 57 | +{ | |
| 58 | + const char * const plugin_name = plugin_info->base_name; | |
| 59 | + const int argc = plugin_info->argc; | |
| 60 | + const struct plugin_argument *argv = plugin_info->argv; | |
| 61 | + int tso = 0; | |
| 62 | + int i; | |
| 63 | + | |
| 64 | + if (!plugin_default_version_check(version, &gcc_version)) { | |
| 65 | + error(G_("incompatible gcc/plugin versions")); | |
| 66 | + return 1; | |
| 67 | + } | |
| 68 | + | |
| 69 | + for (i = 0; i < argc; ++i) { | |
| 70 | + if (!strcmp(argv[i].key, "disable")) | |
| 71 | + return 0; | |
| 72 | + | |
| 73 | + /* all remaining options require a value */ | |
| 74 | + if (!argv[i].value) { | |
| 75 | + error(G_("no value supplied for option '-fplugin-arg-%s-%s'"), | |
| 76 | + plugin_name, argv[i].key); | |
| 77 | + return 1; | |
| 78 | + } | |
| 79 | + | |
| 80 | + if (!strcmp(argv[i].key, "tso")) { | |
| 81 | + tso = atoi(argv[i].value); | |
| 82 | + continue; | |
| 83 | + } | |
| 84 | + | |
| 85 | + if (!strcmp(argv[i].key, "offset")) { | |
| 86 | + canary_offset = atoi(argv[i].value); | |
| 87 | + continue; | |
| 88 | + } | |
| 89 | + error(G_("unknown option '-fplugin-arg-%s-%s'"), | |
| 90 | + plugin_name, argv[i].key); | |
| 91 | + return 1; | |
| 92 | + } | |
| 93 | + | |
| 94 | + /* create the mask that produces the base of the stack */ | |
| 95 | + sp_mask = ~((1U << (12 + tso)) - 1); | |
| 96 | + | |
| 97 | + PASS_INFO(arm_pertask_ssp_rtl, "expand", 1, PASS_POS_INSERT_AFTER); | |
| 98 | + | |
| 99 | + register_callback(plugin_info->base_name, PLUGIN_PASS_MANAGER_SETUP, | |
| 100 | + NULL, &arm_pertask_ssp_rtl_pass_info); | |
| 101 | + | |
| 102 | + return 0; | |
| 103 | +} | |