Operations which write to memory and special purpose registers should be
restricted on systems with integrity guarantees (such as Secure Boot)
and, optionally, to avoid self-destructive behaviors.
Add a config option, XMON_DEFAULT_RO_MODE, to set default xmon behavior.
The kernel cmdline options xmon=ro and xmon=rw override this default.
The following xmon operations are affected:
memops:
disable memmove
disable memset
disable memzcan
memex:
no-op'd mwrite
super_regs:
no-op'd write_spr
bpt_cmds:
disable
proc_call:
disable
Signed-off-by: Christopher M. Riedl <c...@informatik.wtf>
---
v2->v3:
Use XMON_DEFAULT_RO_MODE to set xmon read-only mode
Untangle read-only mode from STRICT_KERNEL_RWX and PAGE_KERNEL_ROX
Update printed msg string for write ops in read-only mode
arch/powerpc/Kconfig.debug | 8 ++++++++
arch/powerpc/xmon/xmon.c | 42 ++++++++++++++++++++++++++++++++++++++
2 files changed, 50 insertions(+)
diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug
index 4e00cb0a5464..8de4823dfb86 100644
--- a/arch/powerpc/Kconfig.debug
+++ b/arch/powerpc/Kconfig.debug
@@ -117,6 +117,14 @@ config XMON_DISASSEMBLY
to say Y here, unless you're building for a memory-constrained
system.
+config XMON_DEFAULT_RO_MODE
+ bool "Restrict xmon to read-only operations"
+ depends on XMON
+ default y
+ help
+ Operate xmon in read-only mode. The cmdline options 'xmon=rw' and
+ 'xmon=ro' override this default.
+
config DEBUGGER
bool
depends on KGDB || XMON
diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index a0f44f992360..ce98c8049eb6 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -80,6 +80,7 @@ static int set_indicator_token = RTAS_UNKNOWN_SERVICE;
#endif
static unsigned long in_xmon __read_mostly = 0;
static int xmon_on = IS_ENABLED(CONFIG_XMON_DEFAULT);
+static bool xmon_is_ro = IS_ENABLED(CONFIG_XMON_DEFAULT_RO_MODE);
static unsigned long adrs;
static int size = 1;
@@ -202,6 +203,8 @@ static void dump_tlb_book3e(void);
#define GETWORD(v) (((v)[0] << 24) + ((v)[1] << 16) + ((v)[2] << 8) +
(v)[3])
#endif
+static const char *xmon_ro_msg = "Operation disabled: xmon in read-only
mode\n";
+
static char *help_string = "\
Commands:\n\
b show breakpoints\n\
@@ -989,6 +992,10 @@ cmds(struct pt_regs *excp)
memlocate();
break;
case 'z':
+ if (xmon_is_ro) {
+ printf(xmon_ro_msg);
+ break;
+ }
memzcan();
break;
case 'i':
@@ -1042,6 +1049,10 @@ cmds(struct pt_regs *excp)
set_lpp_cmd();
break;
case 'b':
+ if (xmon_is_ro) {
+ printf(xmon_ro_msg);
+ break;
+ }
bpt_cmds();
break;
case 'C':
@@ -1055,6 +1066,10 @@ cmds(struct pt_regs *excp)
bootcmds();
break;
case 'p':
+ if (xmon_is_ro) {
+ printf(xmon_ro_msg);
+ break;
+ }
proccall();
break;
case 'P':
@@ -1777,6 +1792,11 @@ read_spr(int n, unsigned long *vp)
static void
write_spr(int n, unsigned long val)
{
+ if (xmon_is_ro) {
+ printf(xmon_ro_msg);
+ return;
+ }
+
if (setjmp(bus_error_jmp) == 0) {
catch_spr_faults = 1;
sync();
@@ -2016,6 +2036,12 @@ mwrite(unsigned long adrs, void *buf, int size)
char *p, *q;
n = 0;
+
+ if (xmon_is_ro) {
+ printf(xmon_ro_msg);
+ return n;
+ }
+
if (setjmp(bus_error_jmp) == 0) {
catch_memory_errors = 1;
sync();
@@ -2884,9 +2910,17 @@ memops(int cmd)
scanhex((void *)&mcount);
switch( cmd ){
case 'm':
+ if (xmon_is_ro) {
+ printf(xmon_ro_msg);
+ break;
+ }
memmove((void *)mdest, (void *)msrc, mcount);
break;
case 's':
+ if (xmon_is_ro) {
+ printf(xmon_ro_msg);
+ break;
+ }
memset((void *)mdest, mval, mcount);
break;
case 'd':
@@ -3796,6 +3830,14 @@ static int __init early_parse_xmon(char *p)
} else if (strncmp(p, "on", 2) == 0) {
xmon_init(1);
xmon_on = 1;
+ } else if (strncmp(p, "rw", 2) == 0) {
+ xmon_init(1);
+ xmon_on = 1;
+ xmon_is_ro = false;
+ } else if (strncmp(p, "ro", 2) == 0) {
+ xmon_init(1);
+ xmon_on = 1;
+ xmon_is_ro = true;
} else if (strncmp(p, "off", 3) == 0)
xmon_on = 0;
else
--
2.21.0
