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powerpc/xmon: add read-only mode 

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 <cmr@informatik.wtf>
Reviewed-by: Oliver O'Halloran <oohall@gmail.com>
Reviewed-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Christopher M. Riedl 2019-04-15 22:26:38 -05:00 committed by Michael Ellerman
parent 5d085ec04a
commit 0acb5f6456
2 changed files with 50 additions and 0 deletions
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8
arch/powerpc/Kconfig.debug
View File

@ -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 by default"
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

42
arch/powerpc/xmon/xmon.c
View File

@ -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();
@ -2880,9 +2906,17 @@ 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':
@ -3792,6 +3826,14 @@ 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