[GIT PULL] x86/debug changes for v4.18
From: Ingo Molnar
Date: Mon Jun 04 2018 - 12:49:16 EST
Linus,
Please pull the latest x86-debug-for-linus git tree from:
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86-debug-for-linus
# HEAD: 4dba072cd097f35fa8f77c49d909ada2b079a4c4 x86/dumpstack: Explain the reasoning for the prologue and buffer size
This tree contains the x86 oops code printing reorganization and cleanups from
Borislav Betkov, with a particular focus in enhancing opcode dumping all around.
Thanks,
Ingo
------------------>
Borislav Petkov (9):
x86/dumpstack: Remove code_bytes
x86/dumpstack: Unexport oops_begin()
x86/dumpstack: Carve out code-dumping into a function
x86/dumpstack: Improve opcodes dumping in the code section
x86/dumpstack: Add loglevel argument to show_opcodes()
x86/fault: Dump user opcode bytes on fatal faults
x86/dumpstack: Add a show_ip() function
x86/dumpstack: Save first regs set for the executive summary
x86/dumpstack: Explain the reasoning for the prologue and buffer size
Documentation/admin-guide/kernel-parameters.txt | 5 -
arch/x86/include/asm/stacktrace.h | 2 +
arch/x86/kernel/dumpstack.c | 144 ++++++++++++------------
arch/x86/kernel/process_32.c | 8 +-
arch/x86/mm/fault.c | 7 +-
5 files changed, 80 insertions(+), 86 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 11fc28ecdb6d..47aa554e41b7 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -587,11 +587,6 @@
Sets the size of memory pool for coherent, atomic dma
allocations, by default set to 256K.
- code_bytes [X86] How many bytes of object code to print
- in an oops report.
- Range: 0 - 8192
- Default: 64
-
com20020= [HW,NET] ARCnet - COM20020 chipset
Format:
<io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
diff --git a/arch/x86/include/asm/stacktrace.h b/arch/x86/include/asm/stacktrace.h
index 133d9425fced..b6dc698f992a 100644
--- a/arch/x86/include/asm/stacktrace.h
+++ b/arch/x86/include/asm/stacktrace.h
@@ -111,4 +111,6 @@ static inline unsigned long caller_frame_pointer(void)
return (unsigned long)frame;
}
+void show_opcodes(u8 *rip, const char *loglvl);
+void show_ip(struct pt_regs *regs, const char *loglvl);
#endif /* _ASM_X86_STACKTRACE_H */
diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index 18fa9d74c182..666a284116ac 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -22,11 +22,14 @@
#include <asm/stacktrace.h>
#include <asm/unwind.h>
+#define OPCODE_BUFSIZE 64
+
int panic_on_unrecovered_nmi;
int panic_on_io_nmi;
-static unsigned int code_bytes = 64;
static int die_counter;
+static struct pt_regs exec_summary_regs;
+
bool in_task_stack(unsigned long *stack, struct task_struct *task,
struct stack_info *info)
{
@@ -69,9 +72,62 @@ static void printk_stack_address(unsigned long address, int reliable,
printk("%s %s%pB\n", log_lvl, reliable ? "" : "? ", (void *)address);
}
+/*
+ * There are a couple of reasons for the 2/3rd prologue, courtesy of Linus:
+ *
+ * In case where we don't have the exact kernel image (which, if we did, we can
+ * simply disassemble and navigate to the RIP), the purpose of the bigger
+ * prologue is to have more context and to be able to correlate the code from
+ * the different toolchains better.
+ *
+ * In addition, it helps in recreating the register allocation of the failing
+ * kernel and thus make sense of the register dump.
+ *
+ * What is more, the additional complication of a variable length insn arch like
+ * x86 warrants having longer byte sequence before rIP so that the disassembler
+ * can "sync" up properly and find instruction boundaries when decoding the
+ * opcode bytes.
+ *
+ * Thus, the 2/3rds prologue and 64 byte OPCODE_BUFSIZE is just a random
+ * guesstimate in attempt to achieve all of the above.
+ */
+void show_opcodes(u8 *rip, const char *loglvl)
+{
+ unsigned int code_prologue = OPCODE_BUFSIZE * 2 / 3;
+ u8 opcodes[OPCODE_BUFSIZE];
+ u8 *ip;
+ int i;
+
+ printk("%sCode: ", loglvl);
+
+ ip = (u8 *)rip - code_prologue;
+ if (probe_kernel_read(opcodes, ip, OPCODE_BUFSIZE)) {
+ pr_cont("Bad RIP value.\n");
+ return;
+ }
+
+ for (i = 0; i < OPCODE_BUFSIZE; i++, ip++) {
+ if (ip == rip)
+ pr_cont("<%02x> ", opcodes[i]);
+ else
+ pr_cont("%02x ", opcodes[i]);
+ }
+ pr_cont("\n");
+}
+
+void show_ip(struct pt_regs *regs, const char *loglvl)
+{
+#ifdef CONFIG_X86_32
+ printk("%sEIP: %pS\n", loglvl, (void *)regs->ip);
+#else
+ printk("%sRIP: %04x:%pS\n", loglvl, (int)regs->cs, (void *)regs->ip);
+#endif
+ show_opcodes((u8 *)regs->ip, loglvl);
+}
+
void show_iret_regs(struct pt_regs *regs)
{
- printk(KERN_DEFAULT "RIP: %04x:%pS\n", (int)regs->cs, (void *)regs->ip);
+ show_ip(regs, KERN_DEFAULT);
printk(KERN_DEFAULT "RSP: %04x:%016lx EFLAGS: %08lx", (int)regs->ss,
regs->sp, regs->flags);
}
@@ -267,7 +323,6 @@ unsigned long oops_begin(void)
bust_spinlocks(1);
return flags;
}
-EXPORT_SYMBOL_GPL(oops_begin);
NOKPROBE_SYMBOL(oops_begin);
void __noreturn rewind_stack_do_exit(int signr);
@@ -287,6 +342,9 @@ void oops_end(unsigned long flags, struct pt_regs *regs, int signr)
raw_local_irq_restore(flags);
oops_exit();
+ /* Executive summary in case the oops scrolled away */
+ __show_regs(&exec_summary_regs, true);
+
if (!signr)
return;
if (in_interrupt())
@@ -305,10 +363,10 @@ NOKPROBE_SYMBOL(oops_end);
int __die(const char *str, struct pt_regs *regs, long err)
{
-#ifdef CONFIG_X86_32
- unsigned short ss;
- unsigned long sp;
-#endif
+ /* Save the regs of the first oops for the executive summary later. */
+ if (!die_counter)
+ exec_summary_regs = *regs;
+
printk(KERN_DEFAULT
"%s: %04lx [#%d]%s%s%s%s%s\n", str, err & 0xffff, ++die_counter,
IS_ENABLED(CONFIG_PREEMPT) ? " PREEMPT" : "",
@@ -318,26 +376,13 @@ int __die(const char *str, struct pt_regs *regs, long err)
IS_ENABLED(CONFIG_PAGE_TABLE_ISOLATION) ?
(boot_cpu_has(X86_FEATURE_PTI) ? " PTI" : " NOPTI") : "");
+ show_regs(regs);
+ print_modules();
+
if (notify_die(DIE_OOPS, str, regs, err,
current->thread.trap_nr, SIGSEGV) == NOTIFY_STOP)
return 1;
- print_modules();
- show_regs(regs);
-#ifdef CONFIG_X86_32
- if (user_mode(regs)) {
- sp = regs->sp;
- ss = regs->ss;
- } else {
- sp = kernel_stack_pointer(regs);
- savesegment(ss, ss);
- }
- printk(KERN_EMERG "EIP: %pS SS:ESP: %04x:%08lx\n",
- (void *)regs->ip, ss, sp);
-#else
- /* Executive summary in case the oops scrolled away */
- printk(KERN_ALERT "RIP: %pS RSP: %016lx\n", (void *)regs->ip, regs->sp);
-#endif
return 0;
}
NOKPROBE_SYMBOL(__die);
@@ -356,30 +401,9 @@ void die(const char *str, struct pt_regs *regs, long err)
oops_end(flags, regs, sig);
}
-static int __init code_bytes_setup(char *s)
-{
- ssize_t ret;
- unsigned long val;
-
- if (!s)
- return -EINVAL;
-
- ret = kstrtoul(s, 0, &val);
- if (ret)
- return ret;
-
- code_bytes = val;
- if (code_bytes > 8192)
- code_bytes = 8192;
-
- return 1;
-}
-__setup("code_bytes=", code_bytes_setup);
-
void show_regs(struct pt_regs *regs)
{
bool all = true;
- int i;
show_regs_print_info(KERN_DEFAULT);
@@ -389,36 +413,8 @@ void show_regs(struct pt_regs *regs)
__show_regs(regs, all);
/*
- * When in-kernel, we also print out the stack and code at the
- * time of the fault..
+ * When in-kernel, we also print out the stack at the time of the fault..
*/
- if (!user_mode(regs)) {
- unsigned int code_prologue = code_bytes * 43 / 64;
- unsigned int code_len = code_bytes;
- unsigned char c;
- u8 *ip;
-
+ if (!user_mode(regs))
show_trace_log_lvl(current, regs, NULL, KERN_DEFAULT);
-
- printk(KERN_DEFAULT "Code: ");
-
- ip = (u8 *)regs->ip - code_prologue;
- if (ip < (u8 *)PAGE_OFFSET || probe_kernel_address(ip, c)) {
- /* try starting at IP */
- ip = (u8 *)regs->ip;
- code_len = code_len - code_prologue + 1;
- }
- for (i = 0; i < code_len; i++, ip++) {
- if (ip < (u8 *)PAGE_OFFSET ||
- probe_kernel_address(ip, c)) {
- pr_cont(" Bad RIP value.");
- break;
- }
- if (ip == (u8 *)regs->ip)
- pr_cont("<%02x> ", c);
- else
- pr_cont("%02x ", c);
- }
- }
- pr_cont("\n");
}
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 5224c6099184..0ae659de21eb 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -76,16 +76,14 @@ void __show_regs(struct pt_regs *regs, int all)
savesegment(gs, gs);
}
- printk(KERN_DEFAULT "EIP: %pS\n", (void *)regs->ip);
- printk(KERN_DEFAULT "EFLAGS: %08lx CPU: %d\n", regs->flags,
- raw_smp_processor_id());
+ show_ip(regs, KERN_DEFAULT);
printk(KERN_DEFAULT "EAX: %08lx EBX: %08lx ECX: %08lx EDX: %08lx\n",
regs->ax, regs->bx, regs->cx, regs->dx);
printk(KERN_DEFAULT "ESI: %08lx EDI: %08lx EBP: %08lx ESP: %08lx\n",
regs->si, regs->di, regs->bp, sp);
- printk(KERN_DEFAULT " DS: %04x ES: %04x FS: %04x GS: %04x SS: %04x\n",
- (u16)regs->ds, (u16)regs->es, (u16)regs->fs, gs, ss);
+ printk(KERN_DEFAULT "DS: %04x ES: %04x FS: %04x GS: %04x SS: %04x EFLAGS: %08lx\n",
+ (u16)regs->ds, (u16)regs->es, (u16)regs->fs, gs, ss, regs->flags);
if (!all)
return;
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 73bd8c95ac71..a3fd94eff04d 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -828,6 +828,8 @@ static inline void
show_signal_msg(struct pt_regs *regs, unsigned long error_code,
unsigned long address, struct task_struct *tsk)
{
+ const char *loglvl = task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG;
+
if (!unhandled_signal(tsk, SIGSEGV))
return;
@@ -835,13 +837,14 @@ show_signal_msg(struct pt_regs *regs, unsigned long error_code,
return;
printk("%s%s[%d]: segfault at %lx ip %px sp %px error %lx",
- task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG,
- tsk->comm, task_pid_nr(tsk), address,
+ loglvl, tsk->comm, task_pid_nr(tsk), address,
(void *)regs->ip, (void *)regs->sp, error_code);
print_vma_addr(KERN_CONT " in ", regs->ip);
printk(KERN_CONT "\n");
+
+ show_opcodes((u8 *)regs->ip, loglvl);
}
static void