| Message ID | 20190803190040.8103-1-cmr@informatik.wtf (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [RFC,v3] powerpc/xmon: Restrict when kernel is locked down | expand |
"Christopher M. Riedl" <cmr@informatik.wtf> writes: > 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. Xmon checks the lockdown > state and takes appropriate action: > > (1) during xmon_setup to prevent 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 re-entry into xmon > > (3) lockdown=integrity -> lockdown=confidentiality > clear all breakpoints, set xmon read-only mode, > prevent re-entry into xmon > > Suggested-by: Andrew Donnellan <ajd@linux.ibm.com> > Signed-off-by: Christopher M. Riedl <cmr@informatik.wtf> > --- > Changes since v1: > - 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 This looks good to me. So I guess we're just waiting on lockdown to go in somewhere. cheers > diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c > index d0620d762a5a..1a5e43d664ca 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 +188,9 @@ static void dump_tlb_44x(void); > static void dump_tlb_book3e(void); > #endif > > +static void clear_all_bpt(void); > +static void xmon_init(int); > + > #ifdef CONFIG_PPC64 > #define REG "%.16lx" > #else > @@ -283,10 +287,41 @@ 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; > + xmon_on = 0; > + xmon_init(0); > + clear_all_bpt(); > + } > + } > + > + 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) > @@ -704,6 +739,9 @@ static int xmon_bpt(struct pt_regs *regs) > struct bpt *bp; > unsigned long offset; > > + if (xmon_is_locked_down()) > + return 0; > + > if ((regs->msr & (MSR_IR|MSR_PR|MSR_64BIT)) != (MSR_IR|MSR_64BIT)) > return 0; > > @@ -735,6 +773,9 @@ static int xmon_sstep(struct pt_regs *regs) > > static int xmon_break_match(struct pt_regs *regs) > { > + if (xmon_is_locked_down()) > + return 0; > + > if ((regs->msr & (MSR_IR|MSR_PR|MSR_64BIT)) != (MSR_IR|MSR_64BIT)) > return 0; > if (dabr.enabled == 0) > @@ -745,6 +786,9 @@ static int xmon_break_match(struct pt_regs *regs) > > static int xmon_iabr_match(struct pt_regs *regs) > { > + if (xmon_is_locked_down()) > + return 0; > + > if ((regs->msr & (MSR_IR|MSR_PR|MSR_64BIT)) != (MSR_IR|MSR_64BIT)) > return 0; > if (iabr == NULL) > @@ -3741,6 +3785,9 @@ static void xmon_init(int enable) > #ifdef CONFIG_MAGIC_SYSRQ > static void sysrq_handle_xmon(int key) > { > + if (xmon_is_locked_down()) > + return; > + > /* ensure xmon is enabled */ > xmon_init(1); > debugger(get_irq_regs()); > @@ -3762,7 +3809,6 @@ 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; > @@ -3784,8 +3830,12 @@ static void clear_all_bpt(void) > printf("xmon: All breakpoints cleared\n"); > } > > +#ifdef CONFIG_DEBUG_FS > static int xmon_dbgfs_set(void *data, u64 val) > { > + if (xmon_is_locked_down()) > + return 0; > + > xmon_on = !!val; > xmon_init(xmon_on); > > @@ -3844,6 +3894,9 @@ early_param("xmon", early_parse_xmon); > > void __init xmon_setup(void) > { > + if (xmon_is_locked_down()) > + return; > + > if (xmon_on) > xmon_init(1); > if (xmon_early) > diff --git a/include/linux/security.h b/include/linux/security.h > index 807dc0d24982..379b74b5d545 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 f6c74cf6a798..79d1799a62ca 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", > }; > > -- > 2.22.0
diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c index d0620d762a5a..1a5e43d664ca 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 +188,9 @@ static void dump_tlb_44x(void); static void dump_tlb_book3e(void); #endif +static void clear_all_bpt(void); +static void xmon_init(int); + #ifdef CONFIG_PPC64 #define REG "%.16lx" #else @@ -283,10 +287,41 @@ 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; + xmon_on = 0; + xmon_init(0); + clear_all_bpt(); + } + } + + 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) @@ -704,6 +739,9 @@ static int xmon_bpt(struct pt_regs *regs) struct bpt *bp; unsigned long offset; + if (xmon_is_locked_down()) + return 0; + if ((regs->msr & (MSR_IR|MSR_PR|MSR_64BIT)) != (MSR_IR|MSR_64BIT)) return 0; @@ -735,6 +773,9 @@ static int xmon_sstep(struct pt_regs *regs) static int xmon_break_match(struct pt_regs *regs) { + if (xmon_is_locked_down()) + return 0; + if ((regs->msr & (MSR_IR|MSR_PR|MSR_64BIT)) != (MSR_IR|MSR_64BIT)) return 0; if (dabr.enabled == 0) @@ -745,6 +786,9 @@ static int xmon_break_match(struct pt_regs *regs) static int xmon_iabr_match(struct pt_regs *regs) { + if (xmon_is_locked_down()) + return 0; + if ((regs->msr & (MSR_IR|MSR_PR|MSR_64BIT)) != (MSR_IR|MSR_64BIT)) return 0; if (iabr == NULL) @@ -3741,6 +3785,9 @@ static void xmon_init(int enable) #ifdef CONFIG_MAGIC_SYSRQ static void sysrq_handle_xmon(int key) { + if (xmon_is_locked_down()) + return; + /* ensure xmon is enabled */ xmon_init(1); debugger(get_irq_regs()); @@ -3762,7 +3809,6 @@ 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; @@ -3784,8 +3830,12 @@ static void clear_all_bpt(void) printf("xmon: All breakpoints cleared\n"); } +#ifdef CONFIG_DEBUG_FS static int xmon_dbgfs_set(void *data, u64 val) { + if (xmon_is_locked_down()) + return 0; + xmon_on = !!val; xmon_init(xmon_on); @@ -3844,6 +3894,9 @@ early_param("xmon", early_parse_xmon); void __init xmon_setup(void) { + if (xmon_is_locked_down()) + return; + if (xmon_on) xmon_init(1); if (xmon_early) diff --git a/include/linux/security.h b/include/linux/security.h index 807dc0d24982..379b74b5d545 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 f6c74cf6a798..79d1799a62ca 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 completely disable xmon when lockdown=confidentiality. Xmon checks the lockdown state and takes appropriate action: (1) during xmon_setup to prevent 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 re-entry into xmon (3) lockdown=integrity -> lockdown=confidentiality clear all breakpoints, set xmon read-only mode, prevent re-entry into xmon Suggested-by: Andrew Donnellan <ajd@linux.ibm.com> Signed-off-by: Christopher M. Riedl <cmr@informatik.wtf> --- Changes since v1: - 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 arch/powerpc/xmon/xmon.c | 59 ++++++++++++++++++++++++++++++++++-- include/linux/security.h | 2 ++ security/lockdown/lockdown.c | 2 ++ 3 files changed, 60 insertions(+), 3 deletions(-)