2198d07c50
All occurrences of the scs_load macro load the value of the shadow call stack pointer from the task which is current at that point. So instead of taking a task struct register argument in the scs_load macro to specify the task struct to load from, let's always reference the current task directly. This should make it much harder to exploit any instruction sequences reloading the shadow call stack pointer register from memory. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Acked-by: Mark Rutland <mark.rutland@arm.com> Reviewed-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/20230109174800.3286265-2-ardb@kernel.org Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
80 lines
1.7 KiB
C
80 lines
1.7 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _ASM_SCS_H
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#define _ASM_SCS_H
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#ifdef __ASSEMBLY__
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#include <asm/asm-offsets.h>
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#include <asm/sysreg.h>
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#ifdef CONFIG_SHADOW_CALL_STACK
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scs_sp .req x18
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.macro scs_load_current
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get_current_task scs_sp
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ldr scs_sp, [scs_sp, #TSK_TI_SCS_SP]
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.endm
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.macro scs_save tsk
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str scs_sp, [\tsk, #TSK_TI_SCS_SP]
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.endm
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#else
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.macro scs_load_current
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.endm
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.macro scs_save tsk
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.endm
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#endif /* CONFIG_SHADOW_CALL_STACK */
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#else
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#include <linux/scs.h>
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#include <asm/cpufeature.h>
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#ifdef CONFIG_UNWIND_PATCH_PAC_INTO_SCS
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static inline bool should_patch_pac_into_scs(void)
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{
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u64 reg;
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/*
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* We only enable the shadow call stack dynamically if we are running
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* on a system that does not implement PAC or BTI. PAC and SCS provide
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* roughly the same level of protection, and BTI relies on the PACIASP
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* instructions serving as landing pads, preventing us from patching
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* those instructions into something else.
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*/
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reg = read_sysreg_s(SYS_ID_AA64ISAR1_EL1);
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if (SYS_FIELD_GET(ID_AA64ISAR1_EL1, APA, reg) |
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SYS_FIELD_GET(ID_AA64ISAR1_EL1, API, reg))
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return false;
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reg = read_sysreg_s(SYS_ID_AA64ISAR2_EL1);
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if (SYS_FIELD_GET(ID_AA64ISAR2_EL1, APA3, reg))
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return false;
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if (IS_ENABLED(CONFIG_ARM64_BTI_KERNEL)) {
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reg = read_sysreg_s(SYS_ID_AA64PFR1_EL1);
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if (reg & (0xf << ID_AA64PFR1_EL1_BT_SHIFT))
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return false;
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}
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return true;
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}
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static inline void dynamic_scs_init(void)
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{
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if (should_patch_pac_into_scs()) {
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pr_info("Enabling dynamic shadow call stack\n");
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static_branch_enable(&dynamic_scs_enabled);
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}
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}
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#else
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static inline void dynamic_scs_init(void) {}
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#endif
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int scs_patch(const u8 eh_frame[], int size);
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#endif /* __ASSEMBLY __ */
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#endif /* _ASM_SCS_H */
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