powerpc/xmon: Check cpu id in commands "c#", "dp#" and "dx#"

[ Upstream commit 8873aab864 ]

All these commands end up peeking into the PACA using the user
originated cpu id as an index. Check the cpu id is valid in order
to prevent xmon to crash. Instead of printing an error, this follows
the same behavior as the "lp s #" command : ignore the buggy cpu id
parameter and fall back to the #-less version of the command.

Signed-off-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/161531347060.252863.10490063933688958044.stgit@bahia.lan
Signed-off-by: Sasha Levin <sashal@kernel.org>

arch/powerpc/xmon/xmon.c

@@ -1214,7 +1214,7 @@ static int cpu_cmd(void)
 	unsigned long cpu, first_cpu, last_cpu;
 	int timeout;
 
-	if (!scanhex(&cpu)) {
+	if (!scanhex(&cpu) || cpu >= num_possible_cpus()) {
 		/* print cpus waiting or in xmon */
 		printf("cpus stopped:");
 		last_cpu = first_cpu = NR_CPUS;
@@ -2571,7 +2571,7 @@ static void dump_pacas(void)
 
 	termch = c;	/* Put c back, it wasn't 'a' */
 
-	if (scanhex(&num))
+	if (scanhex(&num) && num < num_possible_cpus())
 		dump_one_paca(num);
 	else
 		dump_one_paca(xmon_owner);
@@ -2668,7 +2668,7 @@ static void dump_xives(void)
 
 	termch = c;	/* Put c back, it wasn't 'a' */
 
-	if (scanhex(&num))
+	if (scanhex(&num) && num < num_possible_cpus())
 		dump_one_xive(num);
 	else
 		dump_one_xive(xmon_owner);