prctl: cfi: change the branch landing pad prctl()s to be more descriptive

Per Linus' comments requesting the replacement of "INDIR_BR_LP" in the
indirect branch tracking prctl()s with something more readable, and
suggesting the use of the speculation control prctl()s as an exemplar,
reimplement the prctl()s and related constants that control per-task
forward-edge control flow integrity.

This primarily involves two changes.  First, the prctls are
restructured to resemble the style of the speculative execution
workaround control prctls PR_{GET,SET}_SPECULATION_CTRL, to make them
easier to extend in the future.  Second, the "indir_br_lp" abbrevation
is expanded to "branch_landing_pads" to be less telegraphic.  The
kselftest and documentation is adjusted accordingly.

Link: https://lore.kernel.org/linux-riscv/CAHk-=whhSLGZAx3N5jJpb4GLFDqH_QvS07D+6BnkPWmCEzTAgw@mail.gmail.com/
Cc: Deepak Gupta <debug@rivosinc.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mark Brown <broonie@kernel.org>
Signed-off-by: Paul Walmsley <pjw@kernel.org>

1 files changed, 7 insertions, 8 deletions

diff --git a/arch/riscv/kernel/usercfi.c b/arch/riscv/kernel/usercfi.c
index 04ab1eb8df29..2c535737511d 100644
--- a/arch/riscv/kernel/usercfi.c
+++ b/arch/riscv/kernel/usercfi.c
@@ -465,16 +465,14 @@ int arch_prctl_get_branch_landing_pad_state(struct task_struct *t,
 	if (!is_user_lpad_enabled())
 		return -EINVAL;
 
-	/* indirect branch tracking is enabled on the task or not */
-	fcfi_status |= (is_indir_lp_enabled(t) ? PR_INDIR_BR_LP_ENABLE : 0);
+	fcfi_status = (is_indir_lp_enabled(t) ? PR_CFI_ENABLE : PR_CFI_DISABLE);
+	fcfi_status |= (is_indir_lp_locked(t) ? PR_CFI_LOCK : 0);
 
 	return copy_to_user(state, &fcfi_status, sizeof(fcfi_status)) ? -EFAULT : 0;
 }
 
 int arch_prctl_set_branch_landing_pad_state(struct task_struct *t, unsigned long state)
 {
-	bool enable_indir_lp = false;
-
 	if (!is_user_lpad_enabled())
 		return -EINVAL;
 
@@ -482,12 +480,13 @@ int arch_prctl_set_branch_landing_pad_state(struct task_struct *t, unsigned long
 	if (is_indir_lp_locked(t))
 		return -EINVAL;
 
-	/* Reject unknown flags */
-	if (state & ~PR_INDIR_BR_LP_ENABLE)
+	if (!(state & (PR_CFI_ENABLE | PR_CFI_DISABLE)))
+		return -EINVAL;
+
+	if (state & PR_CFI_ENABLE && state & PR_CFI_DISABLE)
 		return -EINVAL;
 
-	enable_indir_lp = (state & PR_INDIR_BR_LP_ENABLE);
-	set_indir_lp_status(t, enable_indir_lp);
+	set_indir_lp_status(t, !!(state & PR_CFI_ENABLE));
 
 	return 0;
 }