Commit be98fcf7 authored by Benjamin Gray's avatar Benjamin Gray Committed by Michael Ellerman
Browse files

powerpc/dexcr: Support userspace ROP protection 



The ISA 3.1B hashst and hashchk instructions use a per-cpu SPR HASHKEYR
to hold a key used in the hash calculation. This key should be different
for each process to make it harder for a malicious process to recreate
valid hash values for a victim process.

Add support for storing a per-thread hash key, and setting/clearing
HASHKEYR appropriately.

Signed-off-by: default avatarBenjamin Gray <bgray@linux.ibm.com>
Reviewed-by: default avatarRussell Currey <ruscur@russell.cc>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230616034846.311705-6-bgray@linux.ibm.com
parent 5bcba4e6

arch/powerpc/include/asm/processor.h

+1 −0
Original line number Diff line number Diff line
@@ -264,6 +264,7 @@ struct thread_struct { 
	unsigned long   mmcr3;

	unsigned long   sier2;

	unsigned long   sier3;

	unsigned long	hashkeyr;



#endif

};

arch/powerpc/kernel/process.c

+17 −0
Original line number Diff line number Diff line
@@ -1182,6 +1182,9 @@ static inline void save_sprs(struct thread_struct *t) 
		 */

		t->tar = mfspr(SPRN_TAR);

	}



	if (cpu_has_feature(CPU_FTR_DEXCR_NPHIE))

		t->hashkeyr = mfspr(SPRN_HASHKEYR);

#endif

}
@@ -1260,6 +1263,10 @@ static inline void restore_sprs(struct thread_struct *old_thread, 
	if (cpu_has_feature(CPU_FTR_P9_TIDR) &&

	    old_thread->tidr != new_thread->tidr)

		mtspr(SPRN_TIDR, new_thread->tidr);



	if (cpu_has_feature(CPU_FTR_DEXCR_NPHIE) &&

	    old_thread->hashkeyr != new_thread->hashkeyr)

		mtspr(SPRN_HASHKEYR, new_thread->hashkeyr);

#endif



}
@@ -1867,6 +1874,10 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args) 
	}



	p->thread.tidr = 0;

#endif

#ifdef CONFIG_PPC_BOOK3S_64

	if (cpu_has_feature(CPU_FTR_DEXCR_NPHIE))

		p->thread.hashkeyr = current->thread.hashkeyr;

#endif

	return 0;

}
@@ -1984,6 +1995,12 @@ void start_thread(struct pt_regs *regs, unsigned long start, unsigned long sp) 
	current->thread.tm_tfiar = 0;

	current->thread.load_tm = 0;

#endif /* CONFIG_PPC_TRANSACTIONAL_MEM */

#ifdef CONFIG_PPC_BOOK3S_64

	if (cpu_has_feature(CPU_FTR_DEXCR_NPHIE)) {

		current->thread.hashkeyr = get_random_long();

		mtspr(SPRN_HASHKEYR, current->thread.hashkeyr);

	}

#endif /* CONFIG_PPC_BOOK3S_64 */

}

EXPORT_SYMBOL(start_thread);