[PATCH v2] powerpc/xmon: add read-only mode
From: Christopher M. Riedl <hidden>
Date: 2019-04-08 03:07:43
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 <redacted> --- 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 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. + 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