lkml.org 
[lkml]   [2020]   [Jan]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 4.19 055/639] powerpc/kgdb: add kgdb_arch_set/remove_breakpoint()
Date
From: Christophe Leroy <christophe.leroy@c-s.fr>

[ Upstream commit fb978ca207743badfe7efd9eebe68bcbb4969f79 ]

Generic implementation fails to remove breakpoints after init
when CONFIG_STRICT_KERNEL_RWX is selected:

[ 13.251285] KGDB: BP remove failed: c001c338
[ 13.259587] kgdbts: ERROR PUT: end of test buffer on 'do_fork_test' line 8 expected OK got $E14#aa
[ 13.268969] KGDB: re-enter exception: ALL breakpoints killed
[ 13.275099] CPU: 0 PID: 1 Comm: init Not tainted 4.18.0-g82bbb913ffd8 #860
[ 13.282836] Call Trace:
[ 13.285313] [c60e1ba0] [c0080ef0] kgdb_handle_exception+0x6f4/0x720 (unreliable)
[ 13.292618] [c60e1c30] [c000e97c] kgdb_handle_breakpoint+0x3c/0x98
[ 13.298709] [c60e1c40] [c000af54] program_check_exception+0x104/0x700
[ 13.305083] [c60e1c60] [c000e45c] ret_from_except_full+0x0/0x4
[ 13.310845] [c60e1d20] [c02a22ac] run_simple_test+0x2b4/0x2d4
[ 13.316532] [c60e1d30] [c0081698] put_packet+0xb8/0x158
[ 13.321694] [c60e1d60] [c00820b4] gdb_serial_stub+0x230/0xc4c
[ 13.327374] [c60e1dc0] [c0080af8] kgdb_handle_exception+0x2fc/0x720
[ 13.333573] [c60e1e50] [c000e928] kgdb_singlestep+0xb4/0xcc
[ 13.339068] [c60e1e70] [c000ae1c] single_step_exception+0x90/0xac
[ 13.345100] [c60e1e80] [c000e45c] ret_from_except_full+0x0/0x4
[ 13.350865] [c60e1f40] [c000e11c] ret_from_syscall+0x0/0x38
[ 13.356346] Kernel panic - not syncing: Recursive entry to debugger

This patch creates powerpc specific version of
kgdb_arch_set_breakpoint() and kgdb_arch_remove_breakpoint()
using patch_instruction()

Fixes: 1e0fc9d1eb2b ("powerpc/Kconfig: Enable STRICT_KERNEL_RWX for some configs")
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/powerpc/include/asm/kgdb.h | 5 +++-
arch/powerpc/kernel/kgdb.c | 43 +++++++++++++++++++++++++++------
2 files changed, 39 insertions(+), 9 deletions(-)

diff --git a/arch/powerpc/include/asm/kgdb.h b/arch/powerpc/include/asm/kgdb.h
index 9db24e77b9f4b..a9e098a3b881f 100644
--- a/arch/powerpc/include/asm/kgdb.h
+++ b/arch/powerpc/include/asm/kgdb.h
@@ -26,9 +26,12 @@
#define BREAK_INSTR_SIZE 4
#define BUFMAX ((NUMREGBYTES * 2) + 512)
#define OUTBUFMAX ((NUMREGBYTES * 2) + 512)
+
+#define BREAK_INSTR 0x7d821008 /* twge r2, r2 */
+
static inline void arch_kgdb_breakpoint(void)
{
- asm(".long 0x7d821008"); /* twge r2, r2 */
+ asm(stringify_in_c(.long BREAK_INSTR));
}
#define CACHE_FLUSH_IS_SAFE 1
#define DBG_MAX_REG_NUM 70
diff --git a/arch/powerpc/kernel/kgdb.c b/arch/powerpc/kernel/kgdb.c
index 35e240a0a4087..59c578f865aa6 100644
--- a/arch/powerpc/kernel/kgdb.c
+++ b/arch/powerpc/kernel/kgdb.c
@@ -24,6 +24,7 @@
#include <asm/processor.h>
#include <asm/machdep.h>
#include <asm/debug.h>
+#include <asm/code-patching.h>
#include <linux/slab.h>

/*
@@ -144,7 +145,7 @@ static int kgdb_handle_breakpoint(struct pt_regs *regs)
if (kgdb_handle_exception(1, SIGTRAP, 0, regs) != 0)
return 0;

- if (*(u32 *) (regs->nip) == *(u32 *) (&arch_kgdb_ops.gdb_bpt_instr))
+ if (*(u32 *)regs->nip == BREAK_INSTR)
regs->nip += BREAK_INSTR_SIZE;

return 1;
@@ -441,16 +442,42 @@ int kgdb_arch_handle_exception(int vector, int signo, int err_code,
return -1;
}

+int kgdb_arch_set_breakpoint(struct kgdb_bkpt *bpt)
+{
+ int err;
+ unsigned int instr;
+ unsigned int *addr = (unsigned int *)bpt->bpt_addr;
+
+ err = probe_kernel_address(addr, instr);
+ if (err)
+ return err;
+
+ err = patch_instruction(addr, BREAK_INSTR);
+ if (err)
+ return -EFAULT;
+
+ *(unsigned int *)bpt->saved_instr = instr;
+
+ return 0;
+}
+
+int kgdb_arch_remove_breakpoint(struct kgdb_bkpt *bpt)
+{
+ int err;
+ unsigned int instr = *(unsigned int *)bpt->saved_instr;
+ unsigned int *addr = (unsigned int *)bpt->bpt_addr;
+
+ err = patch_instruction(addr, instr);
+ if (err)
+ return -EFAULT;
+
+ return 0;
+}
+
/*
* Global data
*/
-struct kgdb_arch arch_kgdb_ops = {
-#ifdef __LITTLE_ENDIAN__
- .gdb_bpt_instr = {0x08, 0x10, 0x82, 0x7d},
-#else
- .gdb_bpt_instr = {0x7d, 0x82, 0x10, 0x08},
-#endif
-};
+struct kgdb_arch arch_kgdb_ops;

static int kgdb_not_implemented(struct pt_regs *regs)
{
--
2.20.1


\
 
 \ /
  Last update: 2020-01-24 12:02    [W:1.768 / U:2.224 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site