Commit 0acb5f64 authored by Christopher M. Riedl's avatar Christopher M. Riedl Committed by Michael Ellerman
Browse files

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: default avatarChristopher M. Riedl <cmr@informatik.wtf>
Reviewed-by: default avatarOliver O'Halloran <oohall@gmail.com>
Reviewed-by: default avatarAndrew Donnellan <andrew.donnellan@au1.ibm.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent 5d085ec0

arch/powerpc/Kconfig.debug

+8 −0
Original line number Diff line number Diff line
@@ -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

arch/powerpc/xmon/xmon.c

+42 −0
Original line number Diff line number Diff line
@@ -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

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