The quilt patch titled Subject: x86/kgdb: convert early breakpoints to poke breakpoints has been removed from the -mm tree. Its filename was x86-kgdb-convert-early-breakpoints-to-poke-breakpoints.patch
This patch was dropped because an updated version will be issued
------------------------------------------------------ From: Florian Rommel mail@florommel.de Subject: x86/kgdb: convert early breakpoints to poke breakpoints Date: Mon, 12 Aug 2024 01:22:07 +0200
Patch series "kgdb: x86: fix breakpoint removal problems".
This series fixes two problems with KGDB on x86 concerning the removal of breakpoints, causing the kernel to hang. Note that breakpoint removal is not only performed when explicitly deleting a breakpoint, but also happens before continuing execution or single stepping.
This patch (of 2):
On x86, after booting, the kernel text is read-only. Then, KGDB has to use the text_poke mechanism to install software breakpoints. KGDB uses a special (x86-specific) breakpoint type for these kinds of breakpoints (BP_POKE_BREAKPOINT). When removing a breakpoint, KGDB always adheres to the breakpoint's original installment method, which is determined by its type.
Before this fix, early (non-"poke") breakpoints could not be removed after the kernel text was set as read-only since the original code patching mechanism was no longer allowed to remove the breakpoints. Eventually, this even caused the kernel to hang (loop between int3 instruction and the function kgdb_skipexception).
With this patch, we convert early breakpoints to "poke" breakpoints after the kernel text has been made read-only. This makes them removable later.
Link: https://lkml.kernel.org/r/20240811232208.234261-1-mail@florommel.de Link: https://lkml.kernel.org/r/20240811232208.234261-2-mail@florommel.de Signed-off-by: Florian Rommel mail@florommel.de Cc: Borislav Petkov bp@alien8.de Cc: Christophe JAILLET christophe.jaillet@wanadoo.fr Cc: Christophe Leroy christophe.leroy@csgroup.eu Cc: Daniel Thompson daniel.thompson@linaro.org Cc: Dave Hansen dave.hansen@linux.intel.com Cc: Douglas Anderson dianders@chromium.org Cc: Geert Uytterhoeven geert+renesas@glider.be Cc: "H. Peter Anvin" hpa@zytor.com Cc: Ingo Molnar mingo@redhat.com Cc: Jason Wessel jason.wessel@windriver.com Cc: Masami Hiramatsu mhiramat@kernel.org Cc: Peter Zijlstra (Intel) peterz@infradead.org Cc: Randy Dunlap rdunlap@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
arch/x86/kernel/kgdb.c | 14 ++++++++++++++ include/linux/kgdb.h | 3 +++ init/main.c | 1 + kernel/debug/debug_core.c | 7 ++++++- 4 files changed, 24 insertions(+), 1 deletion(-)
--- a/arch/x86/kernel/kgdb.c~x86-kgdb-convert-early-breakpoints-to-poke-breakpoints +++ a/arch/x86/kernel/kgdb.c @@ -623,6 +623,20 @@ out: return retval; }
+void kgdb_after_mark_readonly(void) +{ + int i; + + /* Convert all breakpoints in rodata to BP_POKE_BREAKPOINT. */ + for (i = 0; i < KGDB_MAX_BREAKPOINTS; i++) { + if (kgdb_break[i].state != BP_UNDEFINED && + kgdb_break[i].type == BP_BREAKPOINT && + is_kernel_text(kgdb_break[i].bpt_addr)) { + kgdb_break[i].type = BP_POKE_BREAKPOINT; + } + } +} + static void kgdb_hw_overflow_handler(struct perf_event *event, struct perf_sample_data *data, struct pt_regs *regs) { --- a/include/linux/kgdb.h~x86-kgdb-convert-early-breakpoints-to-poke-breakpoints +++ a/include/linux/kgdb.h @@ -98,6 +98,8 @@ extern int dbg_set_reg(int regno, void * # define KGDB_MAX_BREAKPOINTS 1000 #endif
+extern struct kgdb_bkpt kgdb_break[KGDB_MAX_BREAKPOINTS]; + #define KGDB_HW_BREAKPOINT 1
/* @@ -360,6 +362,7 @@ extern bool dbg_is_early; extern void __init dbg_late_init(void); extern void kgdb_panic(const char *msg); extern void kgdb_free_init_mem(void); +extern void kgdb_after_mark_readonly(void); #else /* ! CONFIG_KGDB */ #define in_dbg_master() (0) #define dbg_late_init() --- a/init/main.c~x86-kgdb-convert-early-breakpoints-to-poke-breakpoints +++ a/init/main.c @@ -1441,6 +1441,7 @@ static void mark_readonly(void) mark_rodata_ro(); debug_checkwx(); rodata_test(); + kgdb_after_mark_readonly(); } else if (IS_ENABLED(CONFIG_STRICT_KERNEL_RWX)) { pr_info("Kernel memory protection disabled.\n"); } else if (IS_ENABLED(CONFIG_ARCH_HAS_STRICT_KERNEL_RWX)) { --- a/kernel/debug/debug_core.c~x86-kgdb-convert-early-breakpoints-to-poke-breakpoints +++ a/kernel/debug/debug_core.c @@ -98,7 +98,7 @@ module_param(kgdbreboot, int, 0644); * Holds information about breakpoints in a kernel. These breakpoints are * added and removed by gdb. */ -static struct kgdb_bkpt kgdb_break[KGDB_MAX_BREAKPOINTS] = { +struct kgdb_bkpt kgdb_break[KGDB_MAX_BREAKPOINTS] = { [0 ... KGDB_MAX_BREAKPOINTS-1] = { .state = BP_UNDEFINED } };
@@ -452,6 +452,11 @@ void kgdb_free_init_mem(void) } }
+void __weak kgdb_after_mark_readonly(void) +{ + /* Weak implementation, may be overridden by arch code */ +} + #ifdef CONFIG_KGDB_KDB void kdb_dump_stack_on_cpu(int cpu) { _
Patches currently in -mm which might be from mail@florommel.de are
x86-kgdb-fix-hang-on-failed-breakpoint-removal.patch