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>

2 files changed, 17 insertions, 23 deletions

diff --git a/tools/perf/trace/beauty/include/uapi/linux/prctl.h b/tools/perf/trace/beauty/include/uapi/linux/prctl.h
index 55b0446fff9d..560f99bc4782 100644
--- a/tools/perf/trace/beauty/include/uapi/linux/prctl.h
+++ b/tools/perf/trace/beauty/include/uapi/linux/prctl.h
@@ -397,30 +397,24 @@ struct prctl_mm_map {
 # define PR_RSEQ_SLICE_EXT_ENABLE		0x01
 
 /*
- * Get the current indirect branch tracking configuration for the current
- * thread, this will be the value configured via PR_SET_INDIR_BR_LP_STATUS.
+ * Get or set the control flow integrity (CFI) configuration for the
+ * current thread.
+ *
+ * Some per-thread control flow integrity settings are not yet
+ * controlled through this prctl(); see for example
+ * PR_{GET,SET,LOCK}_SHADOW_STACK_STATUS
  */
-#define PR_GET_INDIR_BR_LP_STATUS      80
-
+#define PR_GET_CFI	80
+#define PR_SET_CFI	81
 /*
- * 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.
+ * Forward-edge CFI variants (excluding ARM64 BTI, which has its own
+ * prctl()s).
  */
-#define PR_SET_INDIR_BR_LP_STATUS      81
-# define PR_INDIR_BR_LP_ENABLE		   (1UL << 0)
+#define PR_CFI_BRANCH_LANDING_PADS	0
+/* Return and control values for PR_{GET,SET}_CFI */
+# define PR_CFI_ENABLE		_BITUL(0)
+# define PR_CFI_DISABLE		_BITUL(1)
+# define PR_CFI_LOCK		_BITUL(2)
 
-/*
- * 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      82
 
 #endif /* _LINUX_PRCTL_H */
diff --git a/tools/testing/selftests/riscv/cfi/cfitests.c b/tools/testing/selftests/riscv/cfi/cfitests.c
index 0dac74b8553c..39d097b6881f 100644
--- a/tools/testing/selftests/riscv/cfi/cfitests.c
+++ b/tools/testing/selftests/riscv/cfi/cfitests.c
@@ -146,11 +146,11 @@ int main(int argc, char *argv[])
 	 * pads for user mode except lighting up a bit in senvcfg via a prctl.
 	 * Enable landing pad support throughout the execution of the test binary.
 	 */
-	ret = my_syscall5(__NR_prctl, PR_GET_INDIR_BR_LP_STATUS, &lpad_status, 0, 0, 0);
+	ret = my_syscall5(__NR_prctl, PR_GET_CFI, PR_CFI_BRANCH_LANDING_PADS, &lpad_status, 0, 0);
 	if (ret)
 		ksft_exit_fail_msg("Get landing pad status failed with %d\n", ret);
 
-	if (!(lpad_status & PR_INDIR_BR_LP_ENABLE))
+	if (!(lpad_status & PR_CFI_ENABLE))
 		ksft_exit_fail_msg("Landing pad is not enabled, should be enabled via glibc\n");
 
 	ret = my_syscall5(__NR_prctl, PR_GET_SHADOW_STACK_STATUS, &ss_status, 0, 0, 0);