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prctl: add arch-agnostic prctl()s for indirect branch tracking

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Three architectures (x86, aarch64, riscv) have support for indirect
branch tracking feature in a very similar fashion. On a very high
level, indirect branch tracking is a CPU feature where CPU tracks
branches which use a memory operand to transfer control. As part of
this tracking, during an indirect branch, the CPU expects a landing
pad instruction on the target PC, and if not found, the CPU raises
some fault (architecture-dependent).

x86 landing pad instr - 'ENDBRANCH'
arch64 landing pad instr - 'BTI'
riscv landing instr - 'lpad'

Given that three major architectures have support for indirect branch
tracking, this patch creates architecture-agnostic 'prctls' to allow
userspace to control this feature.  They are:
 - PR_GET_INDIR_BR_LP_STATUS: Get the current configured status for indirect
   branch tracking.
 - PR_SET_INDIR_BR_LP_STATUS: Set the configuration for indirect branch
   tracking.
   The following status options are allowed:
       - PR_INDIR_BR_LP_ENABLE: Enables indirect branch tracking on user
         thread.
       - PR_INDIR_BR_LP_DISABLE: Disables indirect branch tracking on user
         thread.
 - PR_LOCK_INDIR_BR_LP_STATUS: Locks configured status for indirect branch
   tracking for user thread.

Reviewed-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Zong Li <zong.li@sifive.com>
Signed-off-by: Deepak Gupta <debug@rivosinc.com>
Tested-by: Andreas Korb <andreas.korb@aisec.fraunhofer.de> # QEMU, custom CVA6
Tested-by: Valentin Haudiquet <valentin.haudiquet@canonical.com>
Link: https://patch.msgid.link/20251112-v5_user_cfi_series-v23-13-b55691eacf4f@rivosinc.com
[pjw@kernel.org: cleaned up patch description, code comments]
Signed-off-by: Paul Walmsley <pjw@kernel.org>
This commit is contained in:
Deepak Gupta
2026-01-25 21:09:54 -07:00
committed by Paul Walmsley
parent 61a0200211
commit 5ca243f6e3
3 changed files with 61 additions and 0 deletions
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4
include/linux/cpu.h
View File

@@ -229,4 +229,8 @@ static inline bool cpu_attack_vector_mitigated(enum cpu_attack_vectors v)
#define smt_mitigations SMT_MITIGATIONS_OFF
#endif
int arch_get_indir_br_lp_status(struct task_struct *t, unsigned long __user *status);
int arch_set_indir_br_lp_status(struct task_struct *t, unsigned long status);
int arch_lock_indir_br_lp_status(struct task_struct *t, unsigned long status);
#endif /* _LINUX_CPU_H_ */

27
include/uapi/linux/prctl.h
View File

@@ -386,4 +386,31 @@ struct prctl_mm_map {
# define PR_FUTEX_HASH_SET_SLOTS 1
# define PR_FUTEX_HASH_GET_SLOTS 2
/*
* Get the current indirect branch tracking configuration for the current
* thread, this will be the value configured via PR_SET_INDIR_BR_LP_STATUS.
*/
#define PR_GET_INDIR_BR_LP_STATUS 79
/*
* Set the indirect branch tracking configuration. PR_INDIR_BR_LP_ENABLE will
* enable cpu feature for user thread, to track all indirect branches and ensure
* they land on arch defined landing pad instruction.
* x86 - If enabled, an indirect branch must land on an ENDBRANCH instruction.
* arch64 - If enabled, an indirect branch must land on a BTI instruction.
* riscv - If enabled, an indirect branch must land on an lpad instruction.
* PR_INDIR_BR_LP_DISABLE will disable feature for user thread and indirect
* branches will no more be tracked by cpu to land on arch defined landing pad
* instruction.
*/
#define PR_SET_INDIR_BR_LP_STATUS 80
# define PR_INDIR_BR_LP_ENABLE (1UL << 0)
/*
* Prevent further changes to the specified indirect branch tracking
* configuration. All bits may be locked via this call, including
* undefined bits.
*/
#define PR_LOCK_INDIR_BR_LP_STATUS 81
#endif /* _LINUX_PRCTL_H */

30
kernel/sys.c
View File

@@ -2388,6 +2388,21 @@ int __weak arch_lock_shadow_stack_status(struct task_struct *t, unsigned long st
return -EINVAL;
}
int __weak arch_get_indir_br_lp_status(struct task_struct *t, unsigned long __user *status)
{
return -EINVAL;
}
int __weak arch_set_indir_br_lp_status(struct task_struct *t, unsigned long status)
{
return -EINVAL;
}
int __weak arch_lock_indir_br_lp_status(struct task_struct *t, unsigned long status)
{
return -EINVAL;
}
#define PR_IO_FLUSHER (PF_MEMALLOC_NOIO | PF_LOCAL_THROTTLE)
static int prctl_set_vma(unsigned long opt, unsigned long addr,
@@ -2868,6 +2883,21 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
case PR_FUTEX_HASH:
error = futex_hash_prctl(arg2, arg3, arg4);
break;
case PR_GET_INDIR_BR_LP_STATUS:
if (arg3 || arg4 || arg5)
return -EINVAL;
error = arch_get_indir_br_lp_status(me, (unsigned long __user *)arg2);
break;
case PR_SET_INDIR_BR_LP_STATUS:
if (arg3 || arg4 || arg5)
return -EINVAL;
error = arch_set_indir_br_lp_status(me, arg2);
break;
case PR_LOCK_INDIR_BR_LP_STATUS:
if (arg3 || arg4 || arg5)
return -EINVAL;
error = arch_lock_indir_br_lp_status(me, arg2);
break;
default:
trace_task_prctl_unknown(option, arg2, arg3, arg4, arg5);
error = -EINVAL;