Commit ab7876a9 authored by Dave Martin's avatar Dave Martin Committed by Catalin Marinas
Browse files

arm64: elf: Enable BTI at exec based on ELF program properties 



For BTI protection to be as comprehensive as possible, it is
desirable to have BTI enabled from process startup.  If this is not
done, the process must use mprotect() to enable BTI for each of its
executable mappings, but this is painful to do in the libc startup
code.  It's simpler and more sound to have the kernel do it
instead.

To this end, detect BTI support in the executable (or ELF
interpreter, as appropriate), via the
NT_GNU_PROGRAM_PROPERTY_TYPE_0 note, and tweak the initial prot
flags for the process' executable pages to include PROT_BTI as
appropriate.

Signed-off-by: default avatarMark Brown <broonie@kernel.org>
Signed-off-by: default avatarDave Martin <Dave.Martin@arm.com>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent fe0f6766

arch/arm64/Kconfig

+3 −0
Original line number Diff line number Diff line
@@ -9,6 +9,7 @@ config ARM64 
	select ACPI_MCFG if (ACPI && PCI)

	select ACPI_SPCR_TABLE if ACPI

	select ACPI_PPTT if ACPI

	select ARCH_BINFMT_ELF_STATE

	select ARCH_CLOCKSOURCE_DATA

	select ARCH_HAS_DEBUG_VIRTUAL

	select ARCH_HAS_DEVMEM_IS_ALLOWED
@@ -33,6 +34,7 @@ config ARM64 
	select ARCH_HAS_SYSCALL_WRAPPER

	select ARCH_HAS_TEARDOWN_DMA_OPS if IOMMU_SUPPORT

	select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST

	select ARCH_HAVE_ELF_PROT

	select ARCH_HAVE_NMI_SAFE_CMPXCHG

	select ARCH_INLINE_READ_LOCK if !PREEMPTION

	select ARCH_INLINE_READ_LOCK_BH if !PREEMPTION
@@ -62,6 +64,7 @@ config ARM64 
	select ARCH_INLINE_SPIN_UNLOCK_IRQRESTORE if !PREEMPTION

	select ARCH_KEEP_MEMBLOCK

	select ARCH_USE_CMPXCHG_LOCKREF

	select ARCH_USE_GNU_PROPERTY if BINFMT_ELF

	select ARCH_USE_QUEUED_RWLOCKS

	select ARCH_USE_QUEUED_SPINLOCKS

	select ARCH_SUPPORTS_MEMORY_FAILURE

arch/arm64/include/asm/elf.h

+50 −0
Original line number Diff line number Diff line
@@ -114,7 +114,11 @@ 


#ifndef __ASSEMBLY__



#include <uapi/linux/elf.h>

#include <linux/bug.h>

#include <linux/errno.h>

#include <linux/fs.h>

#include <linux/types.h>

#include <asm/processor.h> /* for signal_minsigstksz, used by ARCH_DLINFO */



typedef unsigned long elf_greg_t;
@@ -224,6 +228,52 @@ extern int aarch32_setup_additional_pages(struct linux_binprm *bprm, 


#endif /* CONFIG_COMPAT */



struct arch_elf_state {

	int flags;

};



#define ARM64_ELF_BTI		(1 << 0)



#define INIT_ARCH_ELF_STATE {			\

	.flags = 0,				\

}



static inline int arch_parse_elf_property(u32 type, const void *data,

					  size_t datasz, bool compat,

					  struct arch_elf_state *arch)

{

	/* No known properties for AArch32 yet */

	if (IS_ENABLED(CONFIG_COMPAT) && compat)

		return 0;



	if (type == GNU_PROPERTY_AARCH64_FEATURE_1_AND) {

		const u32 *p = data;



		if (datasz != sizeof(*p))

			return -ENOEXEC;



		if (system_supports_bti() &&

		    (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI))

			arch->flags |= ARM64_ELF_BTI;

	}



	return 0;

}



static inline int arch_elf_pt_proc(void *ehdr, void *phdr,

				   struct file *f, bool is_interp,

				   struct arch_elf_state *state)

{

	return 0;

}



static inline int arch_check_elf(void *ehdr, bool has_interp,

				 void *interp_ehdr,

				 struct arch_elf_state *state)

{

	return 0;

}



#endif /* !__ASSEMBLY__ */



#endif

arch/arm64/kernel/process.c

+19 −0
Original line number Diff line number Diff line
@@ -11,6 +11,7 @@ 


#include <linux/compat.h>

#include <linux/efi.h>

#include <linux/elf.h>

#include <linux/export.h>

#include <linux/sched.h>

#include <linux/sched/debug.h>
@@ -18,6 +19,7 @@ 
#include <linux/sched/task_stack.h>

#include <linux/kernel.h>

#include <linux/lockdep.h>

#include <linux/mman.h>

#include <linux/mm.h>

#include <linux/stddef.h>

#include <linux/sysctl.h>
@@ -654,3 +656,20 @@ asmlinkage void __sched arm64_preempt_schedule_irq(void) 
	if (system_capabilities_finalized())

		preempt_schedule_irq();

}



#ifdef CONFIG_BINFMT_ELF

int arch_elf_adjust_prot(int prot, const struct arch_elf_state *state,

			 bool has_interp, bool is_interp)

{

	if (is_interp != has_interp)

		return prot;



	if (!(state->flags & ARM64_ELF_BTI))

		return prot;



	if (prot & PROT_EXEC)

		prot |= PROT_BTI;



	return prot;

}

#endif

include/uapi/linux/elf.h

+6 −0
Original line number Diff line number Diff line
@@ -448,4 +448,10 @@ typedef struct elf64_note { 
  Elf64_Word n_type;	/* Content type */

} Elf64_Nhdr;



/* .note.gnu.property types for EM_AARCH64: */

#define GNU_PROPERTY_AARCH64_FEATURE_1_AND	0xc0000000



/* Bits for GNU_PROPERTY_AARCH64_FEATURE_1_BTI */

#define GNU_PROPERTY_AARCH64_FEATURE_1_BTI	(1U << 0)



#endif /* _UAPI_LINUX_ELF_H */

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