| Message ID | 20190828034613.14750-3-cmr@informatik.wtf (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Restrict xmon when kernel is locked down | expand |
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
> 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 >
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", };
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(-)