git: 30b68ecda84e - main - Changes that improve DTrace FBT reliability on freebsd/arm64:

[Robert Watson]

The branch main has been updated by rwatson:

URL: https://cgit.FreeBSD.org/src/commit/?id=30b68ecda84e38648511f5585a6f36b94b167f0d

commit 30b68ecda84e38648511f5585a6f36b94b167f0d
Author:     Robert Watson <rwatson at FreeBSD.org>
AuthorDate: 2021-01-09 08:38:11 +0000
Commit:     Robert Watson <rwatson at FreeBSD.org>
CommitDate: 2021-01-11 15:42:22 +0000

    Changes that improve DTrace FBT reliability on freebsd/arm64:
    
    - Implement a dtrace_getnanouptime(), matching the existing
      dtrace_getnanotime(), to avoid DTrace calling out to a potentially
      instrumentable function.
    
      (These should probably both be under KDTRACE_HOOKS.  Also, it's not clear
      to me that they are correct implementations for the DTrace thread time
      functions they are used in .. fixes for another commit.)
    
    - Don't allow FBT to instrument functions involved in EL1 exception handling
      that are involved in FBT trap processing: handle_el1h_sync() and
      do_el1h_sync().
    
    - Don't allow FBT to instrument DDB and KDB functions, as that makes it
      rather harder to debug FBT problems.
    
    Prior to these changes, use of FBT on FreeBSD/arm64 rapidly led to kernel
    panics due to recursion in DTrace.
    
    Reliable FBT on FreeBSD/arm64 is reliant on another change from @andrew to
    have the aarch64 instrumentor more carefully check that instructions it
    replaces are against the stack pointer, which can otherwise lead to memory
    corruption.  That change remains under review.
    
    MFC after:      2 weeks
    Reviewed by:    andrew, kp, markj (earlier version), jrtc27 (earlier version)
    Differential revision:  https://reviews.freebsd.org/D27766
---
 sys/cddl/dev/dtrace/aarch64/dtrace_subr.c |  3 ++-
 sys/cddl/dev/dtrace/arm/dtrace_subr.c     |  3 ++-
 sys/cddl/dev/dtrace/riscv/dtrace_subr.c   |  3 ++-
 sys/cddl/dev/fbt/aarch64/fbt_isa.c        |  8 ++++++++
 sys/cddl/dev/fbt/fbt.c                    | 11 +++++++++++
 sys/kern/kern_tc.c                        | 15 +++++++++++++++
 6 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/sys/cddl/dev/dtrace/aarch64/dtrace_subr.c b/sys/cddl/dev/dtrace/aarch64/dtrace_subr.c
index 000de0094492..2d59b29b850b 100644
--- a/sys/cddl/dev/dtrace/aarch64/dtrace_subr.c
+++ b/sys/cddl/dev/dtrace/aarch64/dtrace_subr.c
@@ -49,6 +49,7 @@ __FBSDID("$FreeBSD$");
 extern dtrace_id_t	dtrace_probeid_error;
 extern int (*dtrace_invop_jump_addr)(struct trapframe *);
 extern void dtrace_getnanotime(struct timespec *tsp);
+extern void dtrace_getnanouptime(struct timespec *tsp);
 
 int dtrace_invop(uintptr_t, struct trapframe *, uintptr_t);
 void dtrace_invop_init(void);
@@ -163,7 +164,7 @@ dtrace_gethrtime()
 {
 	struct timespec curtime;
 
-	nanouptime(&curtime);
+	dtrace_getnanouptime(&curtime);
 
 	return (curtime.tv_sec * 1000000000UL + curtime.tv_nsec);
 
diff --git a/sys/cddl/dev/dtrace/arm/dtrace_subr.c b/sys/cddl/dev/dtrace/arm/dtrace_subr.c
index 8cd9c9c1f204..e98a9ded5442 100644
--- a/sys/cddl/dev/dtrace/arm/dtrace_subr.c
+++ b/sys/cddl/dev/dtrace/arm/dtrace_subr.c
@@ -54,6 +54,7 @@ __FBSDID("$FreeBSD$");
 extern dtrace_id_t	dtrace_probeid_error;
 extern int (*dtrace_invop_jump_addr)(struct trapframe *);
 extern void dtrace_getnanotime(struct timespec *tsp);
+extern void dtrace_getnanouptime(struct timespec *tsp);
 
 int dtrace_invop(uintptr_t, struct trapframe *, uintptr_t);
 void dtrace_invop_init(void);
@@ -174,7 +175,7 @@ dtrace_gethrtime()
 {
 	struct	timespec curtime;
 
-	nanouptime(&curtime);
+	dtrace_getnanouptime(&curtime);
 
 	return (curtime.tv_sec * 1000000000UL + curtime.tv_nsec);
 
diff --git a/sys/cddl/dev/dtrace/riscv/dtrace_subr.c b/sys/cddl/dev/dtrace/riscv/dtrace_subr.c
index 463465e119f9..c1ac339b3a26 100644
--- a/sys/cddl/dev/dtrace/riscv/dtrace_subr.c
+++ b/sys/cddl/dev/dtrace/riscv/dtrace_subr.c
@@ -52,6 +52,7 @@ __FBSDID("$FreeBSD$");
 extern dtrace_id_t	dtrace_probeid_error;
 extern int (*dtrace_invop_jump_addr)(struct trapframe *);
 extern void dtrace_getnanotime(struct timespec *tsp);
+extern void dtrace_getnanouptime(struct timespec *tsp);
 
 int dtrace_invop(uintptr_t, struct trapframe *);
 void dtrace_invop_init(void);
@@ -165,7 +166,7 @@ dtrace_gethrtime()
 {
 	struct timespec curtime;
 
-	nanouptime(&curtime);
+	dtrace_getnanouptime(&curtime);
 
 	return (curtime.tv_sec * 1000000000UL + curtime.tv_nsec);
 
diff --git a/sys/cddl/dev/fbt/aarch64/fbt_isa.c b/sys/cddl/dev/fbt/aarch64/fbt_isa.c
index 581f390baf89..3c5070785614 100644
--- a/sys/cddl/dev/fbt/aarch64/fbt_isa.c
+++ b/sys/cddl/dev/fbt/aarch64/fbt_isa.c
@@ -96,6 +96,14 @@ fbt_provide_module_function(linker_file_t lf, int symindx,
 	if (fbt_excluded(name))
 		return (0);
 
+	/*
+	 * Instrumenting certain exception handling functions can lead to FBT
+	 * recursion, so exclude from instrumentation.
+	 */
+	 if (strcmp(name, "handle_el1h_sync") == 0 ||
+	    strcmp(name, "do_el1h_sync") == 0)
+		return (1);
+
 	instr = (uint32_t *)(symval->value);
 	limit = (uint32_t *)(symval->value + symval->size);
 
diff --git a/sys/cddl/dev/fbt/fbt.c b/sys/cddl/dev/fbt/fbt.c
index cf5971d2d9bd..a378ae0eb317 100644
--- a/sys/cddl/dev/fbt/fbt.c
+++ b/sys/cddl/dev/fbt/fbt.c
@@ -127,6 +127,17 @@ fbt_excluded(const char *name)
 		return (1);
 	}
 
+	/*
+	 * Omit instrumentation of functions that are probably in DDB.  It
+	 * makes it too hard to debug broken FBT.
+	 *
+	 * NB: kdb_enter() can be excluded, but its call to printf() can't be.
+	 * This is generally OK since we're not yet in debugging context.
+	 */
+	if (strncmp(name, "db_", 3) == 0 ||
+	    strncmp(name, "kdb_", 4) == 0)
+		return (1);
+
 	/*
 	 * Lock owner methods may be called from probe context.
 	 */
diff --git a/sys/kern/kern_tc.c b/sys/kern/kern_tc.c
index 467e5cf8ee3a..cc3219a885ab 100644
--- a/sys/kern/kern_tc.c
+++ b/sys/kern/kern_tc.c
@@ -146,6 +146,7 @@ static void tc_windup(struct bintime *new_boottimebin);
 static void cpu_tick_calibrate(int);
 
 void dtrace_getnanotime(struct timespec *tsp);
+void dtrace_getnanouptime(struct timespec *tsp);
 
 static int
 sysctl_kern_boottime(SYSCTL_HANDLER_ARGS)
@@ -997,6 +998,20 @@ dtrace_getnanotime(struct timespec *tsp)
 	GETTHMEMBER(tsp, th_nanotime);
 }
 
+/*
+ * This is a clone of getnanouptime used for time since boot.
+ * The dtrace_ prefix prevents fbt from creating probes for
+ * it so an uptime that can be safely used in all fbt probes.
+ */
+void
+dtrace_getnanouptime(struct timespec *tsp)
+{
+	struct bintime bt;
+
+	GETTHMEMBER(&bt, th_offset);
+	bintime2timespec(&bt, tsp);
+}
+
 /*
  * System clock currently providing time to the system. Modifiable via sysctl
  * when the FFCLOCK option is defined.