[src/trunk]: src/sys/kern ksyms(4): Modify ksyms_symtabs only at IPL_HIGH.

[riastradh <riastradh%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/ec4d71ebea55
branches:  trunk
changeset: 379461:ec4d71ebea55
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Tue Jun 01 21:11:07 2021 +0000

description:
ksyms(4): Modify ksyms_symtabs only at IPL_HIGH.

This limits the opportunities for ddb to witness an inconsistent
state of the symbol table list.

diffstat:

 sys/kern/kern_ksyms.c |  29 +++++++++++++++++++++++++++--
 1 files changed, 27 insertions(+), 2 deletions(-)

diffs (95 lines):

diff -r a0536e399474 -r ec4d71ebea55 sys/kern/kern_ksyms.c
--- a/sys/kern/kern_ksyms.c     Tue Jun 01 21:10:23 2021 +0000
+++ b/sys/kern/kern_ksyms.c     Tue Jun 01 21:11:07 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: kern_ksyms.c,v 1.90 2021/06/01 21:10:23 riastradh Exp $        */
+/*     $NetBSD: kern_ksyms.c,v 1.91 2021/06/01 21:11:07 riastradh Exp $        */
 
 /*-
  * Copyright (c) 2008 The NetBSD Foundation, Inc.
@@ -73,7 +73,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_ksyms.c,v 1.90 2021/06/01 21:10:23 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_ksyms.c,v 1.91 2021/06/01 21:11:07 riastradh Exp $");
 
 #if defined(_KERNEL) && defined(_KERNEL_OPT)
 #include "opt_copy_symtab.h"
@@ -93,6 +93,7 @@
 #include <sys/atomic.h>
 #include <sys/ksyms.h>
 #include <sys/kernel.h>
+#include <sys/intr.h>
 
 #ifdef DDB
 #include <ddb/db_output.h>
@@ -308,6 +309,7 @@ addsymtab(const char *name, void *symsta
        int i, j, n, nglob;
        char *str;
        int nsyms = symsize / sizeof(Elf_Sym);
+       int s;
 
        /* Sanity check for pre-allocated map table used during startup. */
        if ((nmap == ksyms_nmap) && (nsyms >= KSYMS_MAX_ID)) {
@@ -443,7 +445,14 @@ addsymtab(const char *name, void *symsta
        KASSERT(strcmp(name, "netbsd") == 0 || mutex_owned(&ksyms_lock));
        KASSERT(cold || mutex_owned(&ksyms_lock));
 
+       /*
+        * Ensure ddb never witnesses an inconsistent state of the
+        * queue, unless memory is so corrupt that we crash in
+        * TAILQ_INSERT_TAIL.
+        */
+       s = splhigh();
        TAILQ_INSERT_TAIL(&ksyms_symtabs, tab, sd_queue);
+       splx(s);
 
        ksyms_sizes_calc();
        ksyms_loaded = true;
@@ -772,6 +781,7 @@ ksyms_modunload(const char *name)
 {
        struct ksyms_symtab *st;
        bool do_free = false;
+       int s;
 
        mutex_enter(&ksyms_lock);
        TAILQ_FOREACH(st, &ksyms_symtabs, sd_queue) {
@@ -782,7 +792,14 @@ ksyms_modunload(const char *name)
                st->sd_gone = true;
                ksyms_sizes_calc();
                if (!ksyms_isopen) {
+                       /*
+                        * Ensure ddb never witnesses an inconsistent
+                        * state of the queue, unless memory is so
+                        * corrupt that we crash in TAILQ_REMOVE.
+                        */
+                       s = splhigh();
                        TAILQ_REMOVE(&ksyms_symtabs, st, sd_queue);
+                       splx(s);
                        do_free = true;
                }
                break;
@@ -1015,6 +1032,7 @@ ksymsclose(dev_t dev, int oflags, int de
 {
        struct ksyms_symtab *st, *next;
        TAILQ_HEAD(, ksyms_symtab) to_free = TAILQ_HEAD_INITIALIZER(to_free);
+       int s;
 
        /* Discard references to symbol tables. */
        mutex_enter(&ksyms_lock);
@@ -1022,7 +1040,14 @@ ksymsclose(dev_t dev, int oflags, int de
        ksyms_last_snapshot = NULL;
        TAILQ_FOREACH_SAFE(st, &ksyms_symtabs, sd_queue, next) {
                if (st->sd_gone) {
+                       /*
+                        * Ensure ddb never witnesses an inconsistent
+                        * state of the queue, unless memory is so
+                        * corrupt that we crash in TAILQ_REMOVE.
+                        */
+                       s = splhigh();
                        TAILQ_REMOVE(&ksyms_symtabs, st, sd_queue);
+                       splx(s);
                        TAILQ_INSERT_TAIL(&to_free, st, sd_queue);
                }
        }