From 0acb5f64560a052fd66ab37b212a72964847160f Mon Sep 17 00:00:00 2001 From: "Christopher M. Riedl" Date: Mon, 15 Apr 2019 22:26:38 -0500 Subject: [PATCH] powerpc/xmon: add read-only mode 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_DEFAULT_RO_MODE, to set default xmon behavior. The kernel cmdline options xmon=ro and xmon=rw override this default. 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 Reviewed-by: Oliver O'Halloran Reviewed-by: Andrew Donnellan Signed-off-by: Michael Ellerman --- arch/powerpc/Kconfig.debug | 8 ++++++++ arch/powerpc/xmon/xmon.c | 42 ++++++++++++++++++++++++++++++++++++++ 2 files changed, 50 insertions(+) diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug index e9ae650c8e93..c59920920ddc 100644 --- a/arch/powerpc/Kconfig.debug +++ b/arch/powerpc/Kconfig.debug @@ -117,6 +117,14 @@ config XMON_DISASSEMBLY to say Y here, unless you're building for a memory-constrained system. +config XMON_DEFAULT_RO_MODE + bool "Restrict xmon to read-only operations by default" + depends on XMON + default y + help + Operate xmon in read-only mode. The cmdline options 'xmon=rw' and + 'xmon=ro' override this default. + config DEBUGGER bool depends on KGDB || XMON diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c index e583ed3f6b93..3e7be19aa208 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_DEFAULT_RO_MODE); 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_ro_msg = "Operation disabled: xmon in read-only mode\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_ro_msg); + 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_ro_msg); + 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_ro_msg); + 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_ro_msg); + 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_ro_msg); + return n; + } + if (setjmp(bus_error_jmp) == 0) { catch_memory_errors = 1; sync(); @@ -2880,9 +2906,17 @@ memops(int cmd) scanhex((void *)&mcount); switch( cmd ){ case 'm': + if (xmon_is_ro) { + printf(xmon_ro_msg); + break; + } memmove((void *)mdest, (void *)msrc, mcount); break; case 's': + if (xmon_is_ro) { + printf(xmon_ro_msg); + break; + } memset((void *)mdest, mval, mcount); break; case 'd': @@ -3792,6 +3826,14 @@ 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