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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: Benjamin Gray <bgray@linux.ibm.com>
Reviewed-by: Russell Currey <ruscur@russell.cc>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230616034846.311705-6-bgray@linux.ibm.com
This commit is contained in:
Benjamin Gray 2023-06-19 17:36:26 +10:00 committed by Michael Ellerman
parent 5bcba4e6c1
commit be98fcf7c1
2 changed files with 18 additions and 0 deletions
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1
arch/powerpc/include/asm/processor.h
View File

@ -264,6 +264,7 @@ struct thread_struct {
unsigned long mmcr3;
unsigned long sier2;
unsigned long sier3;
unsigned long hashkeyr;
#endif
};

17
arch/powerpc/kernel/process.c
View File

@ -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);