Commit 3751d3e8 authored by Jason Wessel's avatar Jason Wessel
Browse files

x86,kgdb: Fix DEBUG_RODATA limitation using text_poke() 



There has long been a limitation using software breakpoints with a
kernel compiled with CONFIG_DEBUG_RODATA going back to 2.6.26. For
this particular patch, it will apply cleanly and has been tested all
the way back to 2.6.36.

The kprobes code uses the text_poke() function which accommodates
writing a breakpoint into a read-only page.  The x86 kgdb code can
solve the problem similarly by overriding the default breakpoint
set/remove routines and using text_poke() directly.

The x86 kgdb code will first attempt to use the traditional
probe_kernel_write(), and next try using a the text_poke() function.
The break point install method is tracked such that the correct break
point removal routine will get called later on.

Cc: x86@kernel.org
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: stable@vger.kernel.org # >= 2.6.36
Inspried-by: default avatarMasami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: default avatarJason Wessel <jason.wessel@windriver.com>
parent 98b54aa1

arch/x86/kernel/kgdb.c

+60 −0
Original line number Diff line number Diff line
@@ -43,6 +43,8 @@ 
#include <linux/smp.h>

#include <linux/nmi.h>

#include <linux/hw_breakpoint.h>

#include <linux/uaccess.h>

#include <linux/memory.h>



#include <asm/debugreg.h>

#include <asm/apicdef.h>
@@ -742,6 +744,64 @@ void kgdb_arch_set_pc(struct pt_regs *regs, unsigned long ip) 
	regs->ip = ip;

}



int kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)

{

	int err;

	char opc[BREAK_INSTR_SIZE];



	bpt->type = BP_BREAKPOINT;

	err = probe_kernel_read(bpt->saved_instr, (char *)bpt->bpt_addr,

				BREAK_INSTR_SIZE);

	if (err)

		return err;

	err = probe_kernel_write((char *)bpt->bpt_addr,

				 arch_kgdb_ops.gdb_bpt_instr, BREAK_INSTR_SIZE);

#ifdef CONFIG_DEBUG_RODATA

	if (!err)

		return err;

	/*

	 * It is safe to call text_poke() because normal kernel execution

	 * is stopped on all cores, so long as the text_mutex is not locked.

	 */

	if (mutex_is_locked(&text_mutex))

		return -EBUSY;

	text_poke((void *)bpt->bpt_addr, arch_kgdb_ops.gdb_bpt_instr,

		  BREAK_INSTR_SIZE);

	err = probe_kernel_read(opc, (char *)bpt->bpt_addr, BREAK_INSTR_SIZE);

	if (err)

		return err;

	if (memcmp(opc, arch_kgdb_ops.gdb_bpt_instr, BREAK_INSTR_SIZE))

		return -EINVAL;

	bpt->type = BP_POKE_BREAKPOINT;

#endif /* CONFIG_DEBUG_RODATA */

	return err;

}



int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)

{

#ifdef CONFIG_DEBUG_RODATA

	int err;

	char opc[BREAK_INSTR_SIZE];



	if (bpt->type != BP_POKE_BREAKPOINT)

		goto knl_write;

	/*

	 * It is safe to call text_poke() because normal kernel execution

	 * is stopped on all cores, so long as the text_mutex is not locked.

	 */

	if (mutex_is_locked(&text_mutex))

		goto knl_write;

	text_poke((void *)bpt->bpt_addr, bpt->saved_instr, BREAK_INSTR_SIZE);

	err = probe_kernel_read(opc, (char *)bpt->bpt_addr, BREAK_INSTR_SIZE);

	if (err || memcmp(opc, bpt->saved_instr, BREAK_INSTR_SIZE))

		goto knl_write;

	return err;

knl_write:

#endif /* CONFIG_DEBUG_RODATA */

	return probe_kernel_write((char *)bpt->bpt_addr,

				  (char *)bpt->saved_instr, BREAK_INSTR_SIZE);

}



struct kgdb_arch arch_kgdb_ops = {

	/* Breakpoint instruction: */

	.gdb_bpt_instr		= { 0xcc },

drivers/misc/kgdbts.c

+0 −17
Original line number Diff line number Diff line
@@ -968,22 +968,6 @@ static void run_singlestep_break_test(void) 
	kgdbts_break_test();

}



static void test_debug_rodata(void)

{

#ifdef CONFIG_DEBUG_RODATA

	/* Until there is an api to write to read-only text segments, use

	 * HW breakpoints for the remainder of any tests, else print a

	 * failure message if hw breakpoints do not work.

	 */

	if (!(arch_kgdb_ops.flags & KGDB_HW_BREAKPOINT && hwbreaks_ok)) {

		eprintk("kgdbts: HW breakpoints BROKEN, ending tests\n");

		return;

	}

	force_hwbrks = 1;

	v1printk("kgdbts:Using HW breakpoints for SW breakpoint tests\n");

#endif /* CONFIG_DEBUG_RODATA */

}



static void kgdbts_run_tests(void)

{

	char *ptr;
@@ -1016,7 +1000,6 @@ static void kgdbts_run_tests(void) 
		v1printk("kgdbts:RUN access write breakpoint test\n");

		run_hw_break_test(0);

	}

	test_debug_rodata();



	/* required internal KGDB tests */

	v1printk("kgdbts:RUN plant and detach test\n");

include/linux/kgdb.h

+2 −1
Original line number Diff line number Diff line
@@ -63,7 +63,8 @@ enum kgdb_bptype { 
	BP_HARDWARE_BREAKPOINT,

	BP_WRITE_WATCHPOINT,

	BP_READ_WATCHPOINT,

	BP_ACCESS_WATCHPOINT

	BP_ACCESS_WATCHPOINT,

	BP_POKE_BREAKPOINT,

};



enum kgdb_bpstate {

CRA Git | Maintained and supported by SUSTech CRA and CCSE