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Subject[PATCH 3/5] x86/dumpstack: Improve opcodes dumping in the Code: section
Date
From: Borislav Petkov <bp@suse.de>

The code used to iterate byte-by-byte over the bytes around RIP and that
is expensive: disabling pagefaults around it, copy_from_user, etc...

Make it read the whole buffer of code_bytes size in one go. By default
use a statically allocated 64 bytes buffer. If "code_bytes=" is supplied
on the cmdline a new buffer gets allocated.

Also, do the PAGE_OFFSET check outside of the function because latter
will be reused in other context.

Signed-off-by: Borislav Petkov <bp@suse.de>
---
arch/x86/kernel/dumpstack.c | 44 +++++++++++++++++++++++++++-----------------
1 file changed, 27 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index 954b1dd1c04a..aef0d98cc282 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -22,9 +22,13 @@
#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 unsigned int code_bytes = OPCODE_BUFSIZE;
+static u8 __opc[OPCODE_BUFSIZE];
+static u8 *opcodes = __opc;
static int die_counter;

bool in_task_stack(unsigned long *stack, struct task_struct *task,
@@ -358,8 +362,8 @@ void die(const char *str, struct pt_regs *regs, long err)

static int __init code_bytes_setup(char *s)
{
- ssize_t ret;
unsigned long val;
+ ssize_t ret;

if (!s)
return -EINVAL;
@@ -372,35 +376,37 @@ static int __init code_bytes_setup(char *s)
if (code_bytes > 8192)
code_bytes = 8192;

+ if (code_bytes > OPCODE_BUFSIZE) {
+ u8 *new_buf = kzalloc(code_bytes, GFP_KERNEL);
+ if (!new_buf)
+ return -EINVAL;
+
+ opcodes = new_buf;
+ }
+
return 1;
}
__setup("code_bytes=", code_bytes_setup);

static void show_opcodes(u8 *rip)
{
- unsigned int code_prologue = code_bytes * 43 / 64;
- unsigned int code_len = code_bytes;
- unsigned char c;
+ unsigned int code_prologue = code_bytes * 43 / OPCODE_BUFSIZE;
u8 *ip;
int i;

printk(KERN_DEFAULT "Code: ");

ip = (u8 *)rip - code_prologue;
- if (ip < (u8 *)PAGE_OFFSET || probe_kernel_address(ip, c)) {
- /* try starting at IP */
- ip = (u8 *)rip;
- code_len = code_len - code_prologue + 1;
+ if (probe_kernel_read(opcodes, ip, code_bytes)) {
+ pr_cont(" Bad RIP value.\n");
+ return;
}
- for (i = 0; i < code_len; i++, ip++) {
- if (ip < (u8 *)PAGE_OFFSET || probe_kernel_address(ip, c)) {
- pr_cont(" Bad RIP value.");
- break;
- }
+
+ for (i = 0; i < code_bytes; i++, ip++) {
if (ip == (u8 *)rip)
- pr_cont("<%02x> ", c);
+ pr_cont("<%02x> ", opcodes[i]);
else
- pr_cont("%02x ", c);
+ pr_cont("%02x ", opcodes[i]);
}
pr_cont("\n");
}
@@ -422,6 +428,10 @@ void show_regs(struct pt_regs *regs)
*/
if (!user_mode(regs)) {
show_trace_log_lvl(current, regs, NULL, KERN_DEFAULT);
- show_opcodes((u8 *)regs->ip);
+
+ if (regs->ip < PAGE_OFFSET)
+ pr_cont(" Bad RIP value.\n");
+ else
+ show_opcodes((u8 *)regs->ip);
}
}
--
2.13.0
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