On Mon, Apr 8, 2019 at 1:06 PM Christopher M. Riedl <c...@informatik.wtf> wrote: > > Operations which write to memory and special purpose registers should be > restricted on systems with integrity guarantees (such as Secure Boot) > and, optionally, to avoid self-destructive behaviors. > > Add a config option, XMON_RW, to control default xmon behavior along > with kernel cmdline options xmon=ro and xmon=rw for explicit control. > Use XMON_RW instead of XMON in the condition to set PAGE_KERNEL_TEXT to > allow xmon in read-only mode alongside write-protected kernel text. > XMON_RW defaults to !STRICT_KERNEL_RWX. > > The following xmon operations are affected: > memops: > disable memmove > disable memset > disable memzcan > memex: > no-op'd mwrite > super_regs: > no-op'd write_spr > bpt_cmds: > disable > proc_call: > disable > > Signed-off-by: Christopher M. Riedl <c...@informatik.wtf> > --- > v1->v2: > Use bool type for xmon_is_ro flag > Replace XMON_RO with XMON_RW config option > Make XMON_RW dependent on STRICT_KERNEL_RWX Do you mean make it dependent on XMON?
> Use XMON_RW to control PAGE_KERNEL_TEXT > Add printf in xmon read-only mode when dropping/skipping writes > Disable memzcan (zero-fill memop) in xmon read-only mode > > arch/powerpc/Kconfig.debug | 10 +++++ > arch/powerpc/include/asm/book3s/32/pgtable.h | 5 ++- > arch/powerpc/include/asm/book3s/64/pgtable.h | 5 ++- > arch/powerpc/include/asm/nohash/pgtable.h | 5 ++- > arch/powerpc/xmon/xmon.c | 42 ++++++++++++++++++++ > 5 files changed, 61 insertions(+), 6 deletions(-) > > diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug > index 4e00cb0a5464..0c7f21476018 100644 > --- a/arch/powerpc/Kconfig.debug > +++ b/arch/powerpc/Kconfig.debug > @@ -117,6 +117,16 @@ config XMON_DISASSEMBLY > to say Y here, unless you're building for a memory-constrained > system. > > +config XMON_RW > + bool "Allow xmon read and write operations" > + depends on XMON > + default !STRICT_KERNEL_RWX > + help > + Allow xmon to read and write to memory and special-purpose > registers. > + Conversely, prevent xmon write access when set to N. Read and write > + access can also be explicitly controlled with 'xmon=rw' or > 'xmon=ro' > + (read-only) cmdline options. Default is !STRICT_KERNEL_RWX. Maybe I am a dumb, but I found this *extremely* confusing. Conventionally Kconfig options will control what code is and is not included in the kernel (see XMON_DISASSEMBLY) rather than changing the default behaviour of code. It's not wrong to do so and I'm going to assume that you were following the pattern of XMON_DEFAULT, but I think you need to be a little more clear about what option actually does. Renaming it to XMON_DEFAULT_RO_MODE and re-wording the description to indicate it's a only a mode change would help a lot. Sorry if this comes across as pointless bikeshedding since it's the opposite of what Christophe said in the last patch, but this was a bit of a head scratcher. > config DEBUGGER > bool > depends on KGDB || XMON > diff --git a/arch/powerpc/include/asm/book3s/32/pgtable.h > b/arch/powerpc/include/asm/book3s/32/pgtable.h > index aa8406b8f7ba..615144ad667d 100644 > --- a/arch/powerpc/include/asm/book3s/32/pgtable.h > +++ b/arch/powerpc/include/asm/book3s/32/pgtable.h > @@ -86,8 +86,9 @@ static inline bool pte_user(pte_t pte) > * set breakpoints anywhere, so don't write protect the kernel text > * on platforms where such control is possible. > */ > -#if defined(CONFIG_KGDB) || defined(CONFIG_XMON) || > defined(CONFIG_BDI_SWITCH) ||\ > - defined(CONFIG_KPROBES) || defined(CONFIG_DYNAMIC_FTRACE) > +#if defined(CONFIG_KGDB) || defined(CONFIG_XMON_RW) || \ > + defined(CONFIG_BDI_SWITCH) || defined(CONFIG_KPROBES) || \ > + defined(CONFIG_DYNAMIC_FTRACE) > #define PAGE_KERNEL_TEXT PAGE_KERNEL_X > #else > #define PAGE_KERNEL_TEXT PAGE_KERNEL_ROX > diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h > b/arch/powerpc/include/asm/book3s/64/pgtable.h > index 581f91be9dd4..bc4655122f6b 100644 > --- a/arch/powerpc/include/asm/book3s/64/pgtable.h > +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h > @@ -168,8 +168,9 @@ > * set breakpoints anywhere, so don't write protect the kernel text > * on platforms where such control is possible. > */ > -#if defined(CONFIG_KGDB) || defined(CONFIG_XMON) || > defined(CONFIG_BDI_SWITCH) || \ > - defined(CONFIG_KPROBES) || defined(CONFIG_DYNAMIC_FTRACE) > +#if defined(CONFIG_KGDB) || defined(CONFIG_XMON_RW) || \ > + defined(CONFIG_BDI_SWITCH) || defined(CONFIG_KPROBES) || \ > + defined(CONFIG_DYNAMIC_FTRACE) > #define PAGE_KERNEL_TEXT PAGE_KERNEL_X > #else > #define PAGE_KERNEL_TEXT PAGE_KERNEL_ROX > diff --git a/arch/powerpc/include/asm/nohash/pgtable.h > b/arch/powerpc/include/asm/nohash/pgtable.h > index 1ca1c1864b32..c052931bd243 100644 > --- a/arch/powerpc/include/asm/nohash/pgtable.h > +++ b/arch/powerpc/include/asm/nohash/pgtable.h > @@ -22,8 +22,9 @@ > * set breakpoints anywhere, so don't write protect the kernel text > * on platforms where such control is possible. > */ > -#if defined(CONFIG_KGDB) || defined(CONFIG_XMON) || > defined(CONFIG_BDI_SWITCH) ||\ > - defined(CONFIG_KPROBES) || defined(CONFIG_DYNAMIC_FTRACE) > +#if defined(CONFIG_KGDB) || defined(CONFIG_XMON_RW) || \ > + defined(CONFIG_BDI_SWITCH) || defined(CONFIG_KPROBES) || \ > + defined(CONFIG_DYNAMIC_FTRACE) > #define PAGE_KERNEL_TEXT PAGE_KERNEL_X > #else > #define PAGE_KERNEL_TEXT PAGE_KERNEL_ROX > diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c > index a0f44f992360..224ca0b3506b 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 bool xmon_is_ro = !IS_ENABLED(CONFIG_XMON_RW); > > static unsigned long adrs; > static int size = 1; > @@ -202,6 +203,8 @@ static void dump_tlb_book3e(void); > #define GETWORD(v) (((v)[0] << 24) + ((v)[1] << 16) + ((v)[2] << 8) + > (v)[3]) > #endif > > +static const char *xmon_is_ro_warn = "xmon read-only mode: skipping write\n"; > + > static char *help_string = "\ > Commands:\n\ > b show breakpoints\n\ > @@ -989,6 +992,10 @@ cmds(struct pt_regs *excp) > memlocate(); > break; > case 'z': > + if (xmon_is_ro) { > + printf(xmon_is_ro_warn); > + break; > + } > memzcan(); > break; > case 'i': > @@ -1042,6 +1049,10 @@ cmds(struct pt_regs *excp) > set_lpp_cmd(); > break; > case 'b': > + if (xmon_is_ro) { > + printf(xmon_is_ro_warn); > + break; > + } > bpt_cmds(); > break; > case 'C': > @@ -1055,6 +1066,10 @@ cmds(struct pt_regs *excp) > bootcmds(); > break; > case 'p': > + if (xmon_is_ro) { > + printf(xmon_is_ro_warn); > + break; > + } > proccall(); > break; > case 'P': > @@ -1777,6 +1792,11 @@ read_spr(int n, unsigned long *vp) > static void > write_spr(int n, unsigned long val) > { > + if (xmon_is_ro) { > + printf(xmon_is_ro_warn); > + return; > + } > + > if (setjmp(bus_error_jmp) == 0) { > catch_spr_faults = 1; > sync(); > @@ -2016,6 +2036,12 @@ mwrite(unsigned long adrs, void *buf, int size) > char *p, *q; > > n = 0; > + > + if (xmon_is_ro) { > + printf(xmon_is_ro_warn); > + return n; > + } > + > if (setjmp(bus_error_jmp) == 0) { > catch_memory_errors = 1; > sync(); > @@ -2884,9 +2910,17 @@ memops(int cmd) > scanhex((void *)&mcount); > switch( cmd ){ > case 'm': > + if (xmon_is_ro) { > + printf(xmon_is_ro_warn); > + break; > + } > memmove((void *)mdest, (void *)msrc, mcount); > break; > case 's': > + if (xmon_is_ro) { > + printf(xmon_is_ro_warn); > + break; > + } > memset((void *)mdest, mval, mcount); > break; > case 'd': > @@ -3796,6 +3830,14 @@ static int __init early_parse_xmon(char *p) > } else if (strncmp(p, "on", 2) == 0) { > xmon_init(1); > xmon_on = 1; > + } else if (strncmp(p, "rw", 2) == 0) { > + xmon_init(1); > + xmon_on = 1; > + xmon_is_ro = false; > + } else if (strncmp(p, "ro", 2) == 0) { > + xmon_init(1); > + xmon_on = 1; > + xmon_is_ro = true; > } else if (strncmp(p, "off", 3) == 0) > xmon_on = 0; > else > -- > 2.21.0 >