On 4/4/19 12:02 am, Christopher M Riedl wrote:
On March 29, 2019 at 12:49 AM Andrew Donnellan <andrew.donnel...@au1.ibm.com>
wrote:
On 29/3/19 3:21 pm, cmr wrote:
Operations which write to memory should be restricted on secure systems
and optionally to avoid self-destructive behaviors.
For reference:
-
https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_linuxppc_issues_issues_219&d=DwICaQ&c=jf_iaSHvJObTbx-siA1ZOg&r=-pHOU8dm1U-U1crivyxKr_-xvZrIBB8YUqvA3el0Ee0&m=zNkGBUKLoTqdSUy_VUpM8VLTEqy7sJfIXpWU-ujc6Rc&s=9jgy61R_p5jvtwOKCMFfnhmJegzCIIomcf4I1BRvBPg&e=
-
https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_linuxppc_issues_issues_232&d=DwICaQ&c=jf_iaSHvJObTbx-siA1ZOg&r=-pHOU8dm1U-U1crivyxKr_-xvZrIBB8YUqvA3el0Ee0&m=zNkGBUKLoTqdSUy_VUpM8VLTEqy7sJfIXpWU-ujc6Rc&s=fFYm1ZTaEp6HbeZMV5JEmlbBtDwdehfiW1H3shFoFMM&e=
Perhaps clarify what is meant here by "secure systems".
Otherwise commit message looks good.
I will reword this for the next patch to reflect the verbiage in the referenced
github issue -- ie. Secure Boot and not violating secure boot integrity by
using xmon.
Sounds good.
---
arch/powerpc/Kconfig.debug | 7 +++++++
arch/powerpc/xmon/xmon.c | 24 ++++++++++++++++++++++++
2 files changed, 31 insertions(+)
diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug
index 4e00cb0a5464..33cc01adf4cb 100644
--- a/arch/powerpc/Kconfig.debug
+++ b/arch/powerpc/Kconfig.debug
@@ -117,6 +117,13 @@ config XMON_DISASSEMBLY
to say Y here, unless you're building for a memory-constrained
system.
+config XMON_RO
+ bool "Set xmon read-only mode"
+ depends on XMON
+ default y
+ help
+ Disable state- and memory-altering write operations in xmon.
The meaning of this option is a bit unclear.
From the code - it looks like what this option actually does is enable
RO mode *by default*. In which case it should probably be called
XMON_RO_DEFAULT and the description should note that RW mode can still
be enabled via a cmdline option.
Based on Christophe's feedback the default will change for this option in the
next patch. I will also add the cmdline options to the description for clarity.
Yep, adding a description of the cmdline options is also a good idea.
+
config DEBUGGER
bool
depends on KGDB || XMON
diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index a0f44f992360..c13ee73cdfd4 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 int xmon_ro = IS_ENABLED(CONFIG_XMON_RO);
static unsigned long adrs;
static int size = 1;
@@ -1042,6 +1043,8 @@ cmds(struct pt_regs *excp)
set_lpp_cmd();
break;
case 'b':
+ if (xmon_ro == 1)
+ break;
For all these cases - it would be much better to print an error message
somewhere when we abort due to read-only mode.
I included print messages initially but then thought about how xmon is intended
for "power" users. I can add print statements to avoid confusion and frustration
since the operations are just "silently" dropped -- *if* that aligns with xmon's
"philosophy".
Power users often want a straightforward self-explanatory UX more than
anyone :)
--
Andrew Donnellan OzLabs, ADL Canberra
andrew.donnel...@au1.ibm.com IBM Australia Limited
