Module Name: src
Committed By: riastradh
Date: Sun May 23 08:59:08 UTC 2021
Modified Files:
src/sys/arch/amd64/amd64: db_disasm.c
Log Message:
ddb/amd64: Don't go out of the way to detect invalid addresses.
db_disasm had logic to detect invalid addresses before trying to
disassemble them. But when disassembling a null instruction address,
the logic to detect invalid addresses itself tried to dereference an
invalid address.
db_get_value can already handle this situation gracefully, so there is
no need for this faulty fault-avoidance logic.
Fixes double-fault in ddb on calling null function pointers. With
any luck, this should make diagnosing such bugs easier in the future!
To generate a diff of this commit:
cvs rdiff -u -r1.27 -r1.28 src/sys/arch/amd64/amd64/db_disasm.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/arch/amd64/amd64/db_disasm.c
diff -u src/sys/arch/amd64/amd64/db_disasm.c:1.27 src/sys/arch/amd64/amd64/db_disasm.c:1.28
--- src/sys/arch/amd64/amd64/db_disasm.c:1.27 Sat Mar 9 08:42:25 2019
+++ src/sys/arch/amd64/amd64/db_disasm.c Sun May 23 08:59:08 2021
@@ -1,4 +1,4 @@
-/* $NetBSD: db_disasm.c,v 1.27 2019/03/09 08:42:25 maxv Exp $ */
+/* $NetBSD: db_disasm.c,v 1.28 2021/05/23 08:59:08 riastradh Exp $ */
/*
* Mach Operating System
@@ -33,7 +33,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: db_disasm.c,v 1.27 2019/03/09 08:42:25 maxv Exp $");
+__KERNEL_RCSID(0, "$NetBSD: db_disasm.c,v 1.28 2021/05/23 08:59:08 riastradh Exp $");
#ifndef _KERNEL
#include <sys/types.h>
@@ -1191,33 +1191,8 @@ db_disasm(db_addr_t loc, bool altfmt)
uint64_t imm64;
int len;
struct i_addr address;
-#ifdef _KERNEL
- pt_entry_t *pte, *pde;
-#endif
u_int rex = 0;
-#ifdef _KERNEL
- /*
- * Don't try to disassemble the location if the mapping is invalid.
- * If we do, we'll fault, and end up debugging the debugger!
- * in the case of largepages, "pte" is really the pde and "pde" is
- * really the entry for the pdp itself.
- */
- if ((vaddr_t)loc >= VM_MIN_KERNEL_ADDRESS)
- pte = kvtopte((vaddr_t)loc);
- else
- pte = vtopte((vaddr_t)loc);
- if ((vaddr_t)pte >= VM_MIN_KERNEL_ADDRESS)
- pde = kvtopte((vaddr_t)pte);
- else
- pde = vtopte((vaddr_t)pte);
-
- if ((*pde & PTE_P) == 0 || (*pte & PTE_P) == 0) {
- db_printf("invalid address\n");
- return (loc);
- }
-#endif
-
get_value_inc(inst, loc, 1, false);
short_addr = false;
size = LONG;
