arm64: mask PAC bits of __builtin_return_address
Functions like vmap() record how much memory has been allocated by their callers, and callers are identified using __builtin_return_address(). Once the kernel is using pointer-auth the return address will be signed. This means it will not match any kernel symbol, and will vary between threads even for the same caller. The output of /proc/vmallocinfo in this case may look like, 0x(____ptrval____)-0x(____ptrval____) 20480 0x86e28000100e7c60 pages=4 vmalloc N0=4 0x(____ptrval____)-0x(____ptrval____) 20480 0x86e28000100e7c60 pages=4 vmalloc N0=4 0x(____ptrval____)-0x(____ptrval____) 20480 0xc5c78000100e7c60 pages=4 vmalloc N0=4 The above three 64bit values should be the same symbol name and not different LR values. Use the pre-processor to add logic to clear the PAC to __builtin_return_address() callers. This patch adds a new file asm/compiler.h and is transitively included via include/compiler_types.h on the compiler command line so it is guaranteed to be loaded and the users of this macro will not find a wrong version. Helper macros ptrauth_kernel_pac_mask/ptrauth_clear_pac are created for this purpose and added in this file. Existing macro ptrauth_user_pac_mask moved from asm/pointer_auth.h. Signed-off-by: Amit Daniel Kachhap <amit.kachhap@arm.com> Reviewed-by: James Morse <james.morse@arm.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
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@ -118,6 +118,7 @@ config ARM64
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select HAVE_ALIGNED_STRUCT_PAGE if SLUB
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select HAVE_ARCH_AUDITSYSCALL
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select HAVE_ARCH_BITREVERSE
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select HAVE_ARCH_COMPILER_H
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select HAVE_ARCH_HUGE_VMAP
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select HAVE_ARCH_JUMP_LABEL
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select HAVE_ARCH_JUMP_LABEL_RELATIVE
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24
arch/arm64/include/asm/compiler.h
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24
arch/arm64/include/asm/compiler.h
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@ -0,0 +1,24 @@
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/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef __ASM_COMPILER_H
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#define __ASM_COMPILER_H
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#if defined(CONFIG_ARM64_PTR_AUTH)
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/*
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* The EL0/EL1 pointer bits used by a pointer authentication code.
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* This is dependent on TBI0/TBI1 being enabled, or bits 63:56 would also apply.
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*/
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#define ptrauth_user_pac_mask() GENMASK_ULL(54, vabits_actual)
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#define ptrauth_kernel_pac_mask() GENMASK_ULL(63, vabits_actual)
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/* Valid for EL0 TTBR0 and EL1 TTBR1 instruction pointers */
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#define ptrauth_clear_pac(ptr) \
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((ptr & BIT_ULL(55)) ? (ptr | ptrauth_kernel_pac_mask()) : \
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(ptr & ~ptrauth_user_pac_mask()))
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#define __builtin_return_address(val) \
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(void *)(ptrauth_clear_pac((unsigned long)__builtin_return_address(val)))
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#endif /* CONFIG_ARM64_PTR_AUTH */
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#endif /* __ASM_COMPILER_H */
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@ -68,16 +68,9 @@ static __always_inline void ptrauth_keys_switch_kernel(struct ptrauth_keys_kerne
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extern int ptrauth_prctl_reset_keys(struct task_struct *tsk, unsigned long arg);
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/*
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* The EL0 pointer bits used by a pointer authentication code.
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* This is dependent on TBI0 being enabled, or bits 63:56 would also apply.
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*/
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#define ptrauth_user_pac_mask() GENMASK(54, vabits_actual)
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/* Only valid for EL0 TTBR0 instruction pointers */
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static inline unsigned long ptrauth_strip_insn_pac(unsigned long ptr)
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{
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return ptr & ~ptrauth_user_pac_mask();
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return ptrauth_clear_pac(ptr);
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}
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#define ptrauth_thread_init_user(tsk) \
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