* [PATCH v5 0/2] Restrict xmon when kernel is locked down
@ 2019-08-28 3:46 Christopher M. Riedl
2019-08-28 3:46 ` [PATCH v5 1/2] powerpc/xmon: Allow listing and clearing breakpoints in read-only mode Christopher M. Riedl
2019-08-28 3:46 ` [PATCH v5 2/2] powerpc/xmon: Restrict when kernel is locked down Christopher M. Riedl
0 siblings, 2 replies; 7+ messages in thread
From: Christopher M. Riedl @ 2019-08-28 3:46 UTC (permalink / raw)
To: linuxppc-dev, kernel-hardening; +Cc: ajd
Xmon should be either fully or partially disabled depending on the
kernel lockdown state.
Put xmon into read-only mode for lockdown=integrity and completely
disable xmon when lockdown=confidentiality. Since this can occur
dynamically, there may be pre-existing, active breakpoints in xmon when
transitioning into read-only mode. These breakpoints will still trigger,
so allow them to be listed, but not cleared or altered, using xmon.
Changes since v4:
- Move lockdown state checks into xmon_core
- Allow clearing of breakpoints in xmon read-only mode
- Test simple scenarios (combinations of xmon and lockdown cmdline
options, setting breakpoints and changing lockdown state, etc) in
QEMU and on an actual POWER8 VM
- Rebase onto security/next-lockdown
b602614a81078bf29c82b2671bb96a63488f68d6
Changes since v3:
- Allow active breakpoints to be shown/listed in read-only mode
Changes since v2:
- Rebased onto v36 of https://patchwork.kernel.org/cover/11049461/
(based on: f632a8170a6b667ee4e3f552087588f0fe13c4bb)
- Do not clear existing breakpoints when transitioning from
lockdown=none to lockdown=integrity
- Remove line continuation and dangling quote (confuses checkpatch.pl)
from the xmon command help/usage string
Christopher M. Riedl (2):
powerpc/xmon: Allow listing active breakpoints in read-only mode
powerpc/xmon: Restrict when kernel is locked down
arch/powerpc/xmon/xmon.c | 104 +++++++++++++++++++++++++++--------
include/linux/security.h | 2 +
security/lockdown/lockdown.c | 2 +
3 files changed, 86 insertions(+), 22 deletions(-)
--
2.23.0
^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH v5 1/2] powerpc/xmon: Allow listing and clearing breakpoints in read-only mode
2019-08-28 3:46 [PATCH v5 0/2] Restrict xmon when kernel is locked down Christopher M. Riedl
@ 2019-08-28 3:46 ` Christopher M. Riedl
2019-08-29 6:40 ` Daniel Axtens
2019-08-28 3:46 ` [PATCH v5 2/2] powerpc/xmon: Restrict when kernel is locked down Christopher M. Riedl
1 sibling, 1 reply; 7+ messages in thread
From: Christopher M. Riedl @ 2019-08-28 3:46 UTC (permalink / raw)
To: linuxppc-dev, kernel-hardening; +Cc: ajd
Read-only mode should not prevent listing and clearing any active
breakpoints.
Signed-off-by: Christopher M. Riedl <cmr@informatik.wtf>
---
arch/powerpc/xmon/xmon.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)
diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index d0620d762a5a..a98a354d46ac 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -1045,10 +1045,6 @@ 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':
@@ -1317,11 +1313,16 @@ bpt_cmds(void)
struct bpt *bp;
cmd = inchar();
+
switch (cmd) {
#ifndef CONFIG_PPC_8xx
static const char badaddr[] = "Only kernel addresses are permitted for breakpoints\n";
int mode;
case 'd': /* bd - hardware data breakpoint */
+ if (xmon_is_ro) {
+ printf(xmon_ro_msg);
+ break;
+ }
if (!ppc_breakpoint_available()) {
printf("Hardware data breakpoint not supported on this cpu\n");
break;
@@ -1349,6 +1350,10 @@ bpt_cmds(void)
break;
case 'i': /* bi - hardware instr breakpoint */
+ if (xmon_is_ro) {
+ printf(xmon_ro_msg);
+ break;
+ }
if (!cpu_has_feature(CPU_FTR_ARCH_207S)) {
printf("Hardware instruction breakpoint "
"not supported on this cpu\n");
@@ -1407,7 +1412,7 @@ bpt_cmds(void)
break;
}
termch = cmd;
- if (!scanhex(&a)) {
+ if (xmon_is_ro || !scanhex(&a)) {
/* print all breakpoints */
printf(" type address\n");
if (dabr.enabled) {
--
2.23.0
^ permalink raw reply related [flat|nested] 7+ messages in thread
* [PATCH v5 2/2] powerpc/xmon: Restrict when kernel is locked down
2019-08-28 3:46 [PATCH v5 0/2] Restrict xmon when kernel is locked down Christopher M. Riedl
2019-08-28 3:46 ` [PATCH v5 1/2] powerpc/xmon: Allow listing and clearing breakpoints in read-only mode Christopher M. Riedl
@ 2019-08-28 3:46 ` Christopher M. Riedl
2019-08-29 7:43 ` Daniel Axtens
1 sibling, 1 reply; 7+ messages in thread
From: Christopher M. Riedl @ 2019-08-28 3:46 UTC (permalink / raw)
To: linuxppc-dev, kernel-hardening; +Cc: ajd
Xmon should be either fully or partially disabled depending on the
kernel lockdown state.
Put xmon into read-only mode for lockdown=integrity and prevent user
entry into xmon when lockdown=confidentiality. Xmon checks the lockdown
state on every attempted entry:
(1) during early xmon'ing
(2) when triggered via sysrq
(3) when toggled via debugfs
(4) when triggered via a previously enabled breakpoint
The following lockdown state transitions are handled:
(1) lockdown=none -> lockdown=integrity
set xmon read-only mode
(2) lockdown=none -> lockdown=confidentiality
clear all breakpoints, set xmon read-only mode,
prevent user re-entry into xmon
(3) lockdown=integrity -> lockdown=confidentiality
clear all breakpoints, set xmon read-only mode,
prevent user re-entry into xmon
Suggested-by: Andrew Donnellan <ajd@linux.ibm.com>
Signed-off-by: Christopher M. Riedl <cmr@informatik.wtf>
---
arch/powerpc/xmon/xmon.c | 85 ++++++++++++++++++++++++++++--------
include/linux/security.h | 2 +
security/lockdown/lockdown.c | 2 +
3 files changed, 72 insertions(+), 17 deletions(-)
diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index a98a354d46ac..94a5fada3034 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -25,6 +25,7 @@
#include <linux/nmi.h>
#include <linux/ctype.h>
#include <linux/highmem.h>
+#include <linux/security.h>
#include <asm/debugfs.h>
#include <asm/ptrace.h>
@@ -187,6 +188,8 @@ static void dump_tlb_44x(void);
static void dump_tlb_book3e(void);
#endif
+static void clear_all_bpt(void);
+
#ifdef CONFIG_PPC64
#define REG "%.16lx"
#else
@@ -283,10 +286,38 @@ Commands:\n\
" U show uptime information\n"
" ? help\n"
" # n limit output to n lines per page (for dp, dpa, dl)\n"
-" zr reboot\n\
- zh halt\n"
+" zr reboot\n"
+" zh halt\n"
;
+#ifdef CONFIG_SECURITY
+static bool xmon_is_locked_down(void)
+{
+ static bool lockdown;
+
+ if (!lockdown) {
+ lockdown = !!security_locked_down(LOCKDOWN_XMON_RW);
+ if (lockdown) {
+ printf("xmon: Disabled due to kernel lockdown\n");
+ xmon_is_ro = true;
+ }
+ }
+
+ if (!xmon_is_ro) {
+ xmon_is_ro = !!security_locked_down(LOCKDOWN_XMON_WR);
+ if (xmon_is_ro)
+ printf("xmon: Read-only due to kernel lockdown\n");
+ }
+
+ return lockdown;
+}
+#else /* CONFIG_SECURITY */
+static inline bool xmon_is_locked_down(void)
+{
+ return false;
+}
+#endif
+
static struct pt_regs *xmon_regs;
static inline void sync(void)
@@ -438,7 +469,10 @@ static bool wait_for_other_cpus(int ncpus)
return false;
}
-#endif /* CONFIG_SMP */
+#else /* CONFIG_SMP */
+static inline void get_output_lock(void) {}
+static inline void release_output_lock(void) {}
+#endif
static inline int unrecoverable_excp(struct pt_regs *regs)
{
@@ -455,6 +489,7 @@ static int xmon_core(struct pt_regs *regs, int fromipi)
int cmd = 0;
struct bpt *bp;
long recurse_jmp[JMP_BUF_LEN];
+ bool locked_down;
unsigned long offset;
unsigned long flags;
#ifdef CONFIG_SMP
@@ -465,6 +500,8 @@ static int xmon_core(struct pt_regs *regs, int fromipi)
local_irq_save(flags);
hard_irq_disable();
+ locked_down = xmon_is_locked_down();
+
tracing_enabled = tracing_is_on();
tracing_off();
@@ -516,7 +553,8 @@ static int xmon_core(struct pt_regs *regs, int fromipi)
if (!fromipi) {
get_output_lock();
- excprint(regs);
+ if (!locked_down)
+ excprint(regs);
if (bp) {
printf("cpu 0x%x stopped at breakpoint 0x%tx (",
cpu, BP_NUM(bp));
@@ -568,10 +606,14 @@ static int xmon_core(struct pt_regs *regs, int fromipi)
}
remove_bpts();
disable_surveillance();
- /* for breakpoint or single step, print the current instr. */
- if (bp || TRAP(regs) == 0xd00)
- ppc_inst_dump(regs->nip, 1, 0);
- printf("enter ? for help\n");
+
+ if (!locked_down) {
+ /* for breakpoint or single step, print curr insn */
+ if (bp || TRAP(regs) == 0xd00)
+ ppc_inst_dump(regs->nip, 1, 0);
+ printf("enter ? for help\n");
+ }
+
mb();
xmon_gate = 1;
barrier();
@@ -595,8 +637,9 @@ static int xmon_core(struct pt_regs *regs, int fromipi)
spin_cpu_relax();
touch_nmi_watchdog();
} else {
- cmd = cmds(regs);
- if (cmd != 0) {
+ if (!locked_down)
+ cmd = cmds(regs);
+ if (locked_down || cmd != 0) {
/* exiting xmon */
insert_bpts();
xmon_gate = 0;
@@ -633,13 +676,16 @@ static int xmon_core(struct pt_regs *regs, int fromipi)
"can't continue\n");
remove_bpts();
disable_surveillance();
- /* for breakpoint or single step, print the current instr. */
- if (bp || TRAP(regs) == 0xd00)
- ppc_inst_dump(regs->nip, 1, 0);
- printf("enter ? for help\n");
+ if (!locked_down) {
+ /* for breakpoint or single step, print current insn */
+ if (bp || TRAP(regs) == 0xd00)
+ ppc_inst_dump(regs->nip, 1, 0);
+ printf("enter ? for help\n");
+ }
}
- cmd = cmds(regs);
+ if (!locked_down)
+ cmd = cmds(regs);
insert_bpts();
in_xmon = 0;
@@ -668,7 +714,10 @@ static int xmon_core(struct pt_regs *regs, int fromipi)
}
}
#endif
- insert_cpu_bpts();
+ if (locked_down)
+ clear_all_bpt();
+ else
+ insert_cpu_bpts();
touch_nmi_watchdog();
local_irq_restore(flags);
@@ -3767,7 +3816,6 @@ static int __init setup_xmon_sysrq(void)
device_initcall(setup_xmon_sysrq);
#endif /* CONFIG_MAGIC_SYSRQ */
-#ifdef CONFIG_DEBUG_FS
static void clear_all_bpt(void)
{
int i;
@@ -3786,9 +3834,12 @@ static void clear_all_bpt(void)
dabr.enabled = 0;
}
+ get_output_lock();
printf("xmon: All breakpoints cleared\n");
+ release_output_lock();
}
+#ifdef CONFIG_DEBUG_FS
static int xmon_dbgfs_set(void *data, u64 val)
{
xmon_on = !!val;
diff --git a/include/linux/security.h b/include/linux/security.h
index 429f9f03372b..ba9d308689b6 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -116,12 +116,14 @@ enum lockdown_reason {
LOCKDOWN_MODULE_PARAMETERS,
LOCKDOWN_MMIOTRACE,
LOCKDOWN_DEBUGFS,
+ LOCKDOWN_XMON_WR,
LOCKDOWN_INTEGRITY_MAX,
LOCKDOWN_KCORE,
LOCKDOWN_KPROBES,
LOCKDOWN_BPF_READ,
LOCKDOWN_PERF,
LOCKDOWN_TRACEFS,
+ LOCKDOWN_XMON_RW,
LOCKDOWN_CONFIDENTIALITY_MAX,
};
diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
index 0068cec77c05..db85182d3f11 100644
--- a/security/lockdown/lockdown.c
+++ b/security/lockdown/lockdown.c
@@ -31,12 +31,14 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
[LOCKDOWN_MODULE_PARAMETERS] = "unsafe module parameters",
[LOCKDOWN_MMIOTRACE] = "unsafe mmio",
[LOCKDOWN_DEBUGFS] = "debugfs access",
+ [LOCKDOWN_XMON_WR] = "xmon write access",
[LOCKDOWN_INTEGRITY_MAX] = "integrity",
[LOCKDOWN_KCORE] = "/proc/kcore access",
[LOCKDOWN_KPROBES] = "use of kprobes",
[LOCKDOWN_BPF_READ] = "use of bpf to read kernel RAM",
[LOCKDOWN_PERF] = "unsafe use of perf",
[LOCKDOWN_TRACEFS] = "use of tracefs",
+ [LOCKDOWN_XMON_RW] = "xmon read and write access",
[LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
};
--
2.23.0
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH v5 1/2] powerpc/xmon: Allow listing and clearing breakpoints in read-only mode
2019-08-28 3:46 ` [PATCH v5 1/2] powerpc/xmon: Allow listing and clearing breakpoints in read-only mode Christopher M. Riedl
@ 2019-08-29 6:40 ` Daniel Axtens
2019-08-29 12:38 ` Christopher M Riedl
0 siblings, 1 reply; 7+ messages in thread
From: Daniel Axtens @ 2019-08-29 6:40 UTC (permalink / raw)
To: Christopher M. Riedl, linuxppc-dev, kernel-hardening; +Cc: ajd
Hi Chris,
> Read-only mode should not prevent listing and clearing any active
> breakpoints.
I tested this and it works for me:
Tested-by: Daniel Axtens <dja@axtens.net>
> + if (xmon_is_ro || !scanhex(&a)) {
It took me a while to figure out what this line does: as I understand
it, the 'b' command can also be used to install a breakpoint (as well as
bi/bd). If we are in ro mode or if the input after 'b' doesn't scan as a
hex string, print the list of breakpoints instead. Anyway, I'm now
happy with it, so:
Reviewed-by: Daniel Axtens <dja@axtens.net>
Regards,
Daniel
> /* print all breakpoints */
> printf(" type address\n");
> if (dabr.enabled) {
> --
> 2.23.0
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v5 2/2] powerpc/xmon: Restrict when kernel is locked down
2019-08-28 3:46 ` [PATCH v5 2/2] powerpc/xmon: Restrict when kernel is locked down Christopher M. Riedl
@ 2019-08-29 7:43 ` Daniel Axtens
2019-08-29 12:36 ` Christopher M Riedl
0 siblings, 1 reply; 7+ messages in thread
From: Daniel Axtens @ 2019-08-29 7:43 UTC (permalink / raw)
To: Christopher M. Riedl, linuxppc-dev, kernel-hardening; +Cc: ajd
Hi,
> Xmon should be either fully or partially disabled depending on the
> kernel lockdown state.
I've been kicking the tyres of this, and it seems to work well:
Tested-by: Daniel Axtens <dja@axtens.net>
>
> Put xmon into read-only mode for lockdown=integrity and prevent user
> entry into xmon when lockdown=confidentiality. Xmon checks the lockdown
> state on every attempted entry:
>
> (1) during early xmon'ing
>
> (2) when triggered via sysrq
>
> (3) when toggled via debugfs
>
> (4) when triggered via a previously enabled breakpoint
>
> The following lockdown state transitions are handled:
>
> (1) lockdown=none -> lockdown=integrity
> set xmon read-only mode
>
> (2) lockdown=none -> lockdown=confidentiality
> clear all breakpoints, set xmon read-only mode,
> prevent user re-entry into xmon
>
> (3) lockdown=integrity -> lockdown=confidentiality
> clear all breakpoints, set xmon read-only mode,
> prevent user re-entry into xmon
I have one small nit: if I enter confidentiality mode and then try to
enter xmon, I get 32 messages about clearing the breakpoints each time I
try to enter xmon:
root@dja-guest:~# echo confidentiality > /sys/kernel/security/lockdown
root@dja-guest:~# echo x >/proc/sysrq-trigger
[ 489.585400] sysrq: Entering xmon
xmon: Disabled due to kernel lockdown
xmon: All breakpoints cleared
xmon: All breakpoints cleared
xmon: All breakpoints cleared
xmon: All breakpoints cleared
xmon: All breakpoints cleared
...
Investigating, I see that this is because my vm has 32 vcpus, and I'm
getting one per CPU.
Looking at the call sites, there's only one other caller, so I think you
might be better served with this:
diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index 94a5fada3034..fcaf1d568162 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -3833,10 +3833,6 @@ static void clear_all_bpt(void)
iabr = NULL;
dabr.enabled = 0;
}
-
- get_output_lock();
- printf("xmon: All breakpoints cleared\n");
- release_output_lock();
}
#ifdef CONFIG_DEBUG_FS
@@ -3846,8 +3842,13 @@ static int xmon_dbgfs_set(void *data, u64 val)
xmon_init(xmon_on);
/* make sure all breakpoints removed when disabling */
- if (!xmon_on)
+ if (!xmon_on) {
clear_all_bpt();
+ get_output_lock();
+ printf("xmon: All breakpoints cleared\n");
+ release_output_lock();
+ }
+
return 0;
}
Apart from that:
Reviewed-by: Daniel Axtens <dja@axtens.net>
Regards,
Daniel
> Suggested-by: Andrew Donnellan <ajd@linux.ibm.com>
> Signed-off-by: Christopher M. Riedl <cmr@informatik.wtf>
> ---
> arch/powerpc/xmon/xmon.c | 85 ++++++++++++++++++++++++++++--------
> include/linux/security.h | 2 +
> security/lockdown/lockdown.c | 2 +
> 3 files changed, 72 insertions(+), 17 deletions(-)
>
> diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
> index a98a354d46ac..94a5fada3034 100644
> --- a/arch/powerpc/xmon/xmon.c
> +++ b/arch/powerpc/xmon/xmon.c
> @@ -25,6 +25,7 @@
> #include <linux/nmi.h>
> #include <linux/ctype.h>
> #include <linux/highmem.h>
> +#include <linux/security.h>
>
> #include <asm/debugfs.h>
> #include <asm/ptrace.h>
> @@ -187,6 +188,8 @@ static void dump_tlb_44x(void);
> static void dump_tlb_book3e(void);
> #endif
>
> +static void clear_all_bpt(void);
> +
> #ifdef CONFIG_PPC64
> #define REG "%.16lx"
> #else
> @@ -283,10 +286,38 @@ Commands:\n\
> " U show uptime information\n"
> " ? help\n"
> " # n limit output to n lines per page (for dp, dpa, dl)\n"
> -" zr reboot\n\
> - zh halt\n"
> +" zr reboot\n"
> +" zh halt\n"
> ;
>
> +#ifdef CONFIG_SECURITY
> +static bool xmon_is_locked_down(void)
> +{
> + static bool lockdown;
> +
> + if (!lockdown) {
> + lockdown = !!security_locked_down(LOCKDOWN_XMON_RW);
> + if (lockdown) {
> + printf("xmon: Disabled due to kernel lockdown\n");
> + xmon_is_ro = true;
> + }
> + }
> +
> + if (!xmon_is_ro) {
> + xmon_is_ro = !!security_locked_down(LOCKDOWN_XMON_WR);
> + if (xmon_is_ro)
> + printf("xmon: Read-only due to kernel lockdown\n");
> + }
> +
> + return lockdown;
> +}
> +#else /* CONFIG_SECURITY */
> +static inline bool xmon_is_locked_down(void)
> +{
> + return false;
> +}
> +#endif
> +
> static struct pt_regs *xmon_regs;
>
> static inline void sync(void)
> @@ -438,7 +469,10 @@ static bool wait_for_other_cpus(int ncpus)
>
> return false;
> }
> -#endif /* CONFIG_SMP */
> +#else /* CONFIG_SMP */
> +static inline void get_output_lock(void) {}
> +static inline void release_output_lock(void) {}
> +#endif
>
> static inline int unrecoverable_excp(struct pt_regs *regs)
> {
> @@ -455,6 +489,7 @@ static int xmon_core(struct pt_regs *regs, int fromipi)
> int cmd = 0;
> struct bpt *bp;
> long recurse_jmp[JMP_BUF_LEN];
> + bool locked_down;
> unsigned long offset;
> unsigned long flags;
> #ifdef CONFIG_SMP
> @@ -465,6 +500,8 @@ static int xmon_core(struct pt_regs *regs, int fromipi)
> local_irq_save(flags);
> hard_irq_disable();
>
> + locked_down = xmon_is_locked_down();
> +
> tracing_enabled = tracing_is_on();
> tracing_off();
>
> @@ -516,7 +553,8 @@ static int xmon_core(struct pt_regs *regs, int fromipi)
>
> if (!fromipi) {
> get_output_lock();
> - excprint(regs);
> + if (!locked_down)
> + excprint(regs);
> if (bp) {
> printf("cpu 0x%x stopped at breakpoint 0x%tx (",
> cpu, BP_NUM(bp));
> @@ -568,10 +606,14 @@ static int xmon_core(struct pt_regs *regs, int fromipi)
> }
> remove_bpts();
> disable_surveillance();
> - /* for breakpoint or single step, print the current instr. */
> - if (bp || TRAP(regs) == 0xd00)
> - ppc_inst_dump(regs->nip, 1, 0);
> - printf("enter ? for help\n");
> +
> + if (!locked_down) {
> + /* for breakpoint or single step, print curr insn */
> + if (bp || TRAP(regs) == 0xd00)
> + ppc_inst_dump(regs->nip, 1, 0);
> + printf("enter ? for help\n");
> + }
> +
> mb();
> xmon_gate = 1;
> barrier();
> @@ -595,8 +637,9 @@ static int xmon_core(struct pt_regs *regs, int fromipi)
> spin_cpu_relax();
> touch_nmi_watchdog();
> } else {
> - cmd = cmds(regs);
> - if (cmd != 0) {
> + if (!locked_down)
> + cmd = cmds(regs);
> + if (locked_down || cmd != 0) {
> /* exiting xmon */
> insert_bpts();
> xmon_gate = 0;
> @@ -633,13 +676,16 @@ static int xmon_core(struct pt_regs *regs, int fromipi)
> "can't continue\n");
> remove_bpts();
> disable_surveillance();
> - /* for breakpoint or single step, print the current instr. */
> - if (bp || TRAP(regs) == 0xd00)
> - ppc_inst_dump(regs->nip, 1, 0);
> - printf("enter ? for help\n");
> + if (!locked_down) {
> + /* for breakpoint or single step, print current insn */
> + if (bp || TRAP(regs) == 0xd00)
> + ppc_inst_dump(regs->nip, 1, 0);
> + printf("enter ? for help\n");
> + }
> }
>
> - cmd = cmds(regs);
> + if (!locked_down)
> + cmd = cmds(regs);
>
> insert_bpts();
> in_xmon = 0;
> @@ -668,7 +714,10 @@ static int xmon_core(struct pt_regs *regs, int fromipi)
> }
> }
> #endif
> - insert_cpu_bpts();
> + if (locked_down)
> + clear_all_bpt();
> + else
> + insert_cpu_bpts();
>
> touch_nmi_watchdog();
> local_irq_restore(flags);
> @@ -3767,7 +3816,6 @@ static int __init setup_xmon_sysrq(void)
> device_initcall(setup_xmon_sysrq);
> #endif /* CONFIG_MAGIC_SYSRQ */
>
> -#ifdef CONFIG_DEBUG_FS
> static void clear_all_bpt(void)
> {
> int i;
> @@ -3786,9 +3834,12 @@ static void clear_all_bpt(void)
> dabr.enabled = 0;
> }
>
> + get_output_lock();
> printf("xmon: All breakpoints cleared\n");
> + release_output_lock();
> }
>
> +#ifdef CONFIG_DEBUG_FS
> static int xmon_dbgfs_set(void *data, u64 val)
> {
> xmon_on = !!val;
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 429f9f03372b..ba9d308689b6 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -116,12 +116,14 @@ enum lockdown_reason {
> LOCKDOWN_MODULE_PARAMETERS,
> LOCKDOWN_MMIOTRACE,
> LOCKDOWN_DEBUGFS,
> + LOCKDOWN_XMON_WR,
> LOCKDOWN_INTEGRITY_MAX,
> LOCKDOWN_KCORE,
> LOCKDOWN_KPROBES,
> LOCKDOWN_BPF_READ,
> LOCKDOWN_PERF,
> LOCKDOWN_TRACEFS,
> + LOCKDOWN_XMON_RW,
> LOCKDOWN_CONFIDENTIALITY_MAX,
> };
>
> diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
> index 0068cec77c05..db85182d3f11 100644
> --- a/security/lockdown/lockdown.c
> +++ b/security/lockdown/lockdown.c
> @@ -31,12 +31,14 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
> [LOCKDOWN_MODULE_PARAMETERS] = "unsafe module parameters",
> [LOCKDOWN_MMIOTRACE] = "unsafe mmio",
> [LOCKDOWN_DEBUGFS] = "debugfs access",
> + [LOCKDOWN_XMON_WR] = "xmon write access",
> [LOCKDOWN_INTEGRITY_MAX] = "integrity",
> [LOCKDOWN_KCORE] = "/proc/kcore access",
> [LOCKDOWN_KPROBES] = "use of kprobes",
> [LOCKDOWN_BPF_READ] = "use of bpf to read kernel RAM",
> [LOCKDOWN_PERF] = "unsafe use of perf",
> [LOCKDOWN_TRACEFS] = "use of tracefs",
> + [LOCKDOWN_XMON_RW] = "xmon read and write access",
> [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
> };
>
> --
> 2.23.0
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH v5 2/2] powerpc/xmon: Restrict when kernel is locked down
2019-08-29 7:43 ` Daniel Axtens
@ 2019-08-29 12:36 ` Christopher M Riedl
0 siblings, 0 replies; 7+ messages in thread
From: Christopher M Riedl @ 2019-08-29 12:36 UTC (permalink / raw)
To: Daniel Axtens, linuxppc-dev, kernel-hardening; +Cc: ajd
> On August 29, 2019 at 2:43 AM Daniel Axtens <dja@axtens.net> wrote:
>
>
> Hi,
>
> > Xmon should be either fully or partially disabled depending on the
> > kernel lockdown state.
>
> I've been kicking the tyres of this, and it seems to work well:
>
> Tested-by: Daniel Axtens <dja@axtens.net>
>
Thank you for taking the time to test this!
>
> I have one small nit: if I enter confidentiality mode and then try to
> enter xmon, I get 32 messages about clearing the breakpoints each time I
> try to enter xmon:
>
Ugh, that's annoying. I tested this on a vm w/ 2 vcpus but should have
considered the case of more vcpus :(
>
> root@dja-guest:~# echo confidentiality > /sys/kernel/security/lockdown
> root@dja-guest:~# echo x >/proc/sysrq-trigger
> [ 489.585400] sysrq: Entering xmon
> xmon: Disabled due to kernel lockdown
> xmon: All breakpoints cleared
> xmon: All breakpoints cleared
> xmon: All breakpoints cleared
> xmon: All breakpoints cleared
> xmon: All breakpoints cleared
> ...
>
> Investigating, I see that this is because my vm has 32 vcpus, and I'm
> getting one per CPU.
>
> Looking at the call sites, there's only one other caller, so I think you
> might be better served with this:
>
> diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
> index 94a5fada3034..fcaf1d568162 100644
> --- a/arch/powerpc/xmon/xmon.c
> +++ b/arch/powerpc/xmon/xmon.c
> @@ -3833,10 +3833,6 @@ static void clear_all_bpt(void)
> iabr = NULL;
> dabr.enabled = 0;
> }
> -
> - get_output_lock();
> - printf("xmon: All breakpoints cleared\n");
> - release_output_lock();
> }
>
> #ifdef CONFIG_DEBUG_FS
> @@ -3846,8 +3842,13 @@ static int xmon_dbgfs_set(void *data, u64 val)
> xmon_init(xmon_on);
>
> /* make sure all breakpoints removed when disabling */
> - if (!xmon_on)
> + if (!xmon_on) {
> clear_all_bpt();
> + get_output_lock();
> + printf("xmon: All breakpoints cleared\n");
> + release_output_lock();
> + }
> +
> return 0;
> }
>
Good point, I will add this to the next version, thanks!
>
> Apart from that:
> Reviewed-by: Daniel Axtens <dja@axtens.net>
>
> Regards,
> Daniel
>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v5 1/2] powerpc/xmon: Allow listing and clearing breakpoints in read-only mode
2019-08-29 6:40 ` Daniel Axtens
@ 2019-08-29 12:38 ` Christopher M Riedl
0 siblings, 0 replies; 7+ messages in thread
From: Christopher M Riedl @ 2019-08-29 12:38 UTC (permalink / raw)
To: Daniel Axtens, linuxppc-dev, kernel-hardening; +Cc: ajd
> On August 29, 2019 at 1:40 AM Daniel Axtens <dja@axtens.net> wrote:
>
>
> Hi Chris,
>
> > Read-only mode should not prevent listing and clearing any active
> > breakpoints.
>
> I tested this and it works for me:
>
> Tested-by: Daniel Axtens <dja@axtens.net>
>
> > + if (xmon_is_ro || !scanhex(&a)) {
>
> It took me a while to figure out what this line does: as I understand
> it, the 'b' command can also be used to install a breakpoint (as well as
> bi/bd). If we are in ro mode or if the input after 'b' doesn't scan as a
> hex string, print the list of breakpoints instead. Anyway, I'm now
> happy with it, so:
>
I can add a comment to that effect in the next version. That entire section
of code could probably be cleaned up a bit - but that's for another patch.
Thanks for testing!
>
> Reviewed-by: Daniel Axtens <dja@axtens.net>
>
> Regards,
> Daniel
>
> > /* print all breakpoints */
> > printf(" type address\n");
> > if (dabr.enabled) {
> > --
> > 2.23.0
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2019-08-29 12:39 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-08-28 3:46 [PATCH v5 0/2] Restrict xmon when kernel is locked down Christopher M. Riedl
2019-08-28 3:46 ` [PATCH v5 1/2] powerpc/xmon: Allow listing and clearing breakpoints in read-only mode Christopher M. Riedl
2019-08-29 6:40 ` Daniel Axtens
2019-08-29 12:38 ` Christopher M Riedl
2019-08-28 3:46 ` [PATCH v5 2/2] powerpc/xmon: Restrict when kernel is locked down Christopher M. Riedl
2019-08-29 7:43 ` Daniel Axtens
2019-08-29 12:36 ` Christopher M Riedl
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