I don't think the problem is what you identified.
arch/i386/kernel/ptrace.c:getreg() takes the extra FS,GS offsets into
account and performs special handling for them. I suspect this is because
they are not stable per-thread registers and not saved into the register
structure on an interrupt or system call.
ptrace.c:getreg() ...
switch (regno >> 2) {
case FS:
retval = child->thread.fs;
break;
case GS:
retval = child->thread.gs;
break;
case DS:
case ES:
case SS:
case CS:
retval = 0xffff;
/* fall through */
default:
if (regno > GS*4) // *** Adusts for missing FS,GS fields *** //
regno -= 2*4;
regno = regno - sizeof(struct pt_regs);
retval &= get_stack_long(child, regno);
}
-----Original Message-----
From: linux-kernel-owner@vger.kernel.org
[mailto:linux-kernel-owner@vger.kernel.org]On Behalf Of Gian-Yan Xu
Sent: Monday, October 15, 2001 5:12 PM
To: linux-kernel@vger.kernel.org
Subject: ptrace bug
Today I try to get register's value via ptrace(PTRACE_GETREGS, ...),
but only EBX, ECX, EDX, ESI, EDI, EBP, EAX registers are correct.
I notice that file /usr/src/linux/include/asm/ptrace.h:
#define FS 9
#define GS 10
but in the declare of struct pt_regs:
struct pt_regs {
long ebx;
long ecx;
long edx;
long esi;
long edi;
long ebp;
long eax;
int xds;
int xes;
long orig_eax;
long eip;
int xcs;
long eflags;
long esp;
int xss;
};
There is no xfs/xgs member in that struct, and the #define FRAME_SIZE 17
is not match the number of member in the pt_regs struct.
In addition, in the ptrace.c:
case PTRACE_GETREGS: { /* Get all gp regs from the child. */
if (!access_ok(VERIFY_WRITE, (unsigned *)data,
FRAME_SIZE*sizeo(long))) {
ret = -EIO;
break;
}
for ( i = 0; i < FRAME_SIZE*sizeof(long); i += sizeof(long) ) {
__put_user(getreg(child, i),(unsigned long *) data);
data += sizeof(long);
}
ret = 0;
FRAME_SIZE*sizeof(long) is larger than sizeof(struct pt_regs),
the ptrace() will overwrite the data of parent process!
To fix the bug, try this patch:
--- ptrace.h.orig Mon Oct 15 21:00:48 2001
+++ ptrace.h Mon Oct 15 21:05:56 2001
@@ -33,6 +33,8 @@
long eax;
int xds;
int xes;
+ int xfs;
+ int xgs;
long orig_eax;
long eip;
int xcs;
-- Best regards, Gian-Yain Xu. (kids@linux.ee.tku.edu.tw)- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
This archive was generated by hypermail 2b29 : Mon Oct 15 2001 - 21:00:58 EST