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SubjectRe: Valgrinding the kernel?
On Fri, Jul 06, 2007 at 10:30:19AM -0700, Dan Kegel wrote:
> Could you give it a shot?

OK, after ripping out the code that broke valgrind last time (patch
below), I get this:

==27590== Warning: set address range perms: large range 516194304, a 0, v 0
vex x86->IR: unhandled instruction bytes: 0xF3 0xAF 0x74 0x9
==27590== Your program just tried to execute an instruction that Valgrind
==27590== did not recognise. There are two possible reasons for this.
==27590== 1. Your program has a bug and erroneously jumped to a non-code
==27590== location. If you are running Memcheck and you just saw a
==27590== warning about a bad jump, it's probably your program's fault.
==27590== 2. The instruction is legitimate but Valgrind doesn't handle it,
==27590== i.e. it's Valgrind's fault. If you think this is the case or
==27590== you are not sure, please let us know.
==27590== Either way, Valgrind will now raise a SIGILL signal which will
==27590== probably kill your program.
==27590==

> Maybe the problems after that will be more pedestrian.

Doesn't look like it.

FWIW, that instruction is repz scas. In an earlier valgrind effort in
2002, I hit repe scas
(http://www.goop.org/~jeremy/valgrind/76-repe-scas.patch), so maybe
something similar is needed here.

> I'm willing to focus a little effort on this.

I guess you'll have to fix valgrind's various bugs. See, simple :)

Jeff

--
Work email - jdike at linux dot intel dot com


Index: linux-2.6.21-mm/arch/um/os-Linux/start_up.c
===================================================================
--- linux-2.6.21-mm.orig/arch/um/os-Linux/start_up.c 2007-07-02 21:11:33.000000000 -0400
+++ linux-2.6.21-mm/arch/um/os-Linux/start_up.c 2007-07-06 15:16:47.000000000 -0400
@@ -43,54 +43,6 @@
#include "registers.h"
#endif

-static int ptrace_child(void *arg)
-{
- int ret;
- int pid = os_getpid(), ppid = getppid();
- int sc_result;
-
- change_sig(SIGWINCH, 0);
- if(ptrace(PTRACE_TRACEME, 0, 0, 0) < 0){
- perror("ptrace");
- os_kill_process(pid, 0);
- }
- kill(pid, SIGSTOP);
-
- /*This syscall will be intercepted by the parent. Don't call more than
- * once, please.*/
- sc_result = os_getpid();
-
- if (sc_result == pid)
- ret = 1; /*Nothing modified by the parent, we are running
- normally.*/
- else if (sc_result == ppid)
- ret = 0; /*Expected in check_ptrace and check_sysemu when they
- succeed in modifying the stack frame*/
- else
- ret = 2; /*Serious trouble! This could be caused by a bug in
- host 2.6 SKAS3/2.6 patch before release -V6, together
- with a bug in the UML code itself.*/
- _exit(ret);
-}
-
-static void fatal_perror(char *str)
-{
- perror(str);
- exit(1);
-}
-
-static void fatal(char *fmt, ...)
-{
- va_list list;
-
- va_start(list, fmt);
- vprintf(fmt, list);
- va_end(list);
- fflush(stdout);
-
- exit(1);
-}
-
static void non_fatal(char *fmt, ...)
{
va_list list;
@@ -101,64 +53,6 @@ static void non_fatal(char *fmt, ...)
fflush(stdout);
}

-static int start_ptraced_child(void **stack_out)
-{
- void *stack;
- unsigned long sp;
- int pid, n, status;
-
- stack = mmap(NULL, UM_KERN_PAGE_SIZE,
- PROT_READ | PROT_WRITE | PROT_EXEC,
- MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
- if(stack == MAP_FAILED)
- fatal_perror("check_ptrace : mmap failed");
- sp = (unsigned long) stack + UM_KERN_PAGE_SIZE - sizeof(void *);
- pid = clone(ptrace_child, (void *) sp, SIGCHLD, NULL);
- if(pid < 0)
- fatal_perror("start_ptraced_child : clone failed");
- CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED));
- if(n < 0)
- fatal_perror("check_ptrace : clone failed");
- if(!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGSTOP))
- fatal("check_ptrace : expected SIGSTOP, got status = %d",
- status);
-
- *stack_out = stack;
- return pid;
-}
-
-/* When testing for SYSEMU support, if it is one of the broken versions, we
- * must just avoid using sysemu, not panic, but only if SYSEMU features are
- * broken.
- * So only for SYSEMU features we test mustpanic, while normal host features
- * must work anyway!
- */
-static int stop_ptraced_child(int pid, void *stack, int exitcode,
- int mustexit)
-{
- int status, n, ret = 0;
-
- if(ptrace(PTRACE_CONT, pid, 0, 0) < 0)
- fatal_perror("stop_ptraced_child : ptrace failed");
- CATCH_EINTR(n = waitpid(pid, &status, 0));
- if(!WIFEXITED(status) || (WEXITSTATUS(status) != exitcode)) {
- int exit_with = WEXITSTATUS(status);
- if (exit_with == 2)
- non_fatal("check_ptrace : child exited with status 2. "
- "\nDisabling SYSEMU support.\n");
- non_fatal("check_ptrace : child exited with exitcode %d, while "
- "expecting %d; status 0x%x\n", exit_with,
- exitcode, status);
- if (mustexit)
- exit(1);
- ret = -1;
- }
-
- if(munmap(stack, UM_KERN_PAGE_SIZE) < 0)
- fatal_perror("check_ptrace : munmap failed");
- return ret;
-}
-
/* Changed only during early boot */
int ptrace_faultinfo = 1;
int ptrace_ldt = 1;
@@ -207,131 +101,23 @@ __uml_setup("nosysemu", nosysemu_cmd_par

static void __init check_sysemu(void)
{
- void *stack;
- unsigned long regs[MAX_REG_NR];
- int pid, n, status, count=0;
-
non_fatal("Checking syscall emulation patch for ptrace...");
- sysemu_supported = 0;
- pid = start_ptraced_child(&stack);
-
- if(ptrace(PTRACE_SYSEMU, pid, 0, 0) < 0)
- goto fail;
-
- CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED));
- if (n < 0)
- fatal_perror("check_sysemu : wait failed");
- if(!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGTRAP))
- fatal("check_sysemu : expected SIGTRAP, got status = %d",
- status);
-
- if(ptrace(PTRACE_GETREGS, pid, 0, regs) < 0)
- fatal_perror("check_sysemu : PTRACE_GETREGS failed");
- if(PT_SYSCALL_NR(regs) != __NR_getpid){
- non_fatal("check_sysemu got system call number %d, "
- "expected %d...", PT_SYSCALL_NR(regs), __NR_getpid);
- goto fail;
- }
-
- n = ptrace(PTRACE_POKEUSR, pid, PT_SYSCALL_RET_OFFSET, os_getpid());
- if(n < 0){
- non_fatal("check_sysemu : failed to modify system call "
- "return");
- goto fail;
- }
-
- if (stop_ptraced_child(pid, stack, 0, 0) < 0)
- goto fail_stopped;
-
sysemu_supported = 1;
non_fatal("OK\n");
set_using_sysemu(!force_sysemu_disabled);

non_fatal("Checking advanced syscall emulation patch for ptrace...");
- pid = start_ptraced_child(&stack);
-
- if((ptrace(PTRACE_OLDSETOPTIONS, pid, 0,
- (void *) PTRACE_O_TRACESYSGOOD) < 0))
- fatal_perror("check_ptrace: PTRACE_OLDSETOPTIONS failed");
-
- while(1){
- count++;
- if(ptrace(PTRACE_SYSEMU_SINGLESTEP, pid, 0, 0) < 0)
- goto fail;
- CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED));
- if(n < 0)
- fatal_perror("check_ptrace : wait failed");
-
- if(WIFSTOPPED(status) && (WSTOPSIG(status) == (SIGTRAP|0x80))){
- if (!count)
- fatal("check_ptrace : SYSEMU_SINGLESTEP "
- "doesn't singlestep");
- n = ptrace(PTRACE_POKEUSR, pid, PT_SYSCALL_RET_OFFSET,
- os_getpid());
- if(n < 0)
- fatal_perror("check_sysemu : failed to modify "
- "system call return");
- break;
- }
- else if(WIFSTOPPED(status) && (WSTOPSIG(status) == SIGTRAP))
- count++;
- else
- fatal("check_ptrace : expected SIGTRAP or "
- "(SIGTRAP | 0x80), got status = %d", status);
- }
- if (stop_ptraced_child(pid, stack, 0, 0) < 0)
- goto fail_stopped;
-
sysemu_supported = 2;
non_fatal("OK\n");

if ( !force_sysemu_disabled )
set_using_sysemu(sysemu_supported);
return;
-
-fail:
- stop_ptraced_child(pid, stack, 1, 0);
-fail_stopped:
- non_fatal("missing\n");
}

static void __init check_ptrace(void)
{
- void *stack;
- int pid, syscall, n, status;
-
non_fatal("Checking that ptrace can change system call numbers...");
- pid = start_ptraced_child(&stack);
-
- if((ptrace(PTRACE_OLDSETOPTIONS, pid, 0,
- (void *) PTRACE_O_TRACESYSGOOD) < 0))
- fatal_perror("check_ptrace: PTRACE_OLDSETOPTIONS failed");
-
- while(1){
- if(ptrace(PTRACE_SYSCALL, pid, 0, 0) < 0)
- fatal_perror("check_ptrace : ptrace failed");
-
- CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED));
- if(n < 0)
- fatal_perror("check_ptrace : wait failed");
-
- if(!WIFSTOPPED(status) ||
- (WSTOPSIG(status) != (SIGTRAP | 0x80)))
- fatal("check_ptrace : expected (SIGTRAP|0x80), "
- "got status = %d", status);
-
- syscall = ptrace(PTRACE_PEEKUSR, pid, PT_SYSCALL_NR_OFFSET,
- 0);
- if(syscall == __NR_getpid){
- n = ptrace(PTRACE_POKEUSR, pid, PT_SYSCALL_NR_OFFSET,
- __NR_getppid);
- if(n < 0)
- fatal_perror("check_ptrace : failed to modify "
- "system call");
- break;
- }
- }
- stop_ptraced_child(pid, stack, 0, 1);
non_fatal("OK\n");
check_sysemu();
}
@@ -411,63 +197,15 @@ __uml_setup("noptraceldt", noptraceldt_c
#ifdef UML_CONFIG_MODE_SKAS
static inline void check_skas3_ptrace_faultinfo(void)
{
- struct ptrace_faultinfo fi;
- void *stack;
- int pid, n;
-
non_fatal(" - PTRACE_FAULTINFO...");
- pid = start_ptraced_child(&stack);
-
- n = ptrace(PTRACE_FAULTINFO, pid, 0, &fi);
- if (n < 0) {
- ptrace_faultinfo = 0;
- if(errno == EIO)
- non_fatal("not found\n");
- else
- perror("not found");
- }
- else {
- if (!ptrace_faultinfo)
- non_fatal("found but disabled on command line\n");
- else
- non_fatal("found\n");
- }
-
- init_registers(pid);
- stop_ptraced_child(pid, stack, 1, 1);
+ non_fatal("not found\n");
}

static inline void check_skas3_ptrace_ldt(void)
{
#ifdef PTRACE_LDT
- void *stack;
- int pid, n;
- unsigned char ldtbuf[40];
- struct ptrace_ldt ldt_op = (struct ptrace_ldt) {
- .func = 2, /* read default ldt */
- .ptr = ldtbuf,
- .bytecount = sizeof(ldtbuf)};
-
non_fatal(" - PTRACE_LDT...");
- pid = start_ptraced_child(&stack);
-
- n = ptrace(PTRACE_LDT, pid, 0, (unsigned long) &ldt_op);
- if (n < 0) {
- if(errno == EIO)
- non_fatal("not found\n");
- else {
- perror("not found");
- }
- ptrace_ldt = 0;
- }
- else {
- if(ptrace_ldt)
- non_fatal("found\n");
- else
- non_fatal("found, but use is disabled\n");
- }
-
- stop_ptraced_child(pid, stack, 1, 1);
+ non_fatal("not found\n");
#else
/* PTRACE_LDT might be disabled via cmdline option.
* We want to override this, else we might use the stub
-
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