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x86: remove last user of get_segment_eip
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is_prefetch was the last user of get_segment_eip and only on
X86_32.  This function returned the faulting instruction's
address and set the upper segment limit.

Instead, use the convert_ip_to_linear helper and rely on
probe_kernel_address to do the segment checks which was
already done everywhere the segment limit was being checked
on X86_32.

Remove get_segment_eip as well.

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Harvey Harrison authored and Ingo Molnar committed Jan 30, 2008
1 parent 37cd9cf commit f2857ce
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Showing 4 changed files with 8 additions and 112 deletions.
84 changes: 0 additions & 84 deletions arch/x86/kernel/step.c
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Original file line number Diff line number Diff line change
Expand Up @@ -5,90 +5,6 @@
#include <linux/mm.h>
#include <linux/ptrace.h>

#ifdef CONFIG_X86_32
#include <linux/uaccess.h>

#include <asm/desc.h>

/*
* Return EIP plus the CS segment base. The segment limit is also
* adjusted, clamped to the kernel/user address space (whichever is
* appropriate), and returned in *eip_limit.
*
* The segment is checked, because it might have been changed by another
* task between the original faulting instruction and here.
*
* If CS is no longer a valid code segment, or if EIP is beyond the
* limit, or if it is a kernel address when CS is not a kernel segment,
* then the returned value will be greater than *eip_limit.
*
* This is slow, but is very rarely executed.
*/
unsigned long get_segment_eip(struct pt_regs *regs,
unsigned long *eip_limit)
{
unsigned long ip = regs->ip;
unsigned seg = regs->cs & 0xffff;
u32 seg_ar, seg_limit, base, *desc;

/* Unlikely, but must come before segment checks. */
if (unlikely(regs->flags & VM_MASK)) {
base = seg << 4;
*eip_limit = base + 0xffff;
return base + (ip & 0xffff);
}

/* The standard kernel/user address space limit. */
*eip_limit = user_mode(regs) ? USER_DS.seg : KERNEL_DS.seg;

/* By far the most common cases. */
if (likely(SEGMENT_IS_FLAT_CODE(seg)))
return ip;

/* Check the segment exists, is within the current LDT/GDT size,
that kernel/user (ring 0..3) has the appropriate privilege,
that it's a code segment, and get the limit. */
__asm__("larl %3,%0; lsll %3,%1"
: "=&r" (seg_ar), "=r" (seg_limit) : "0" (0), "rm" (seg));
if ((~seg_ar & 0x9800) || ip > seg_limit) {
*eip_limit = 0;
return 1; /* So that returned ip > *eip_limit. */
}

/* Get the GDT/LDT descriptor base.
When you look for races in this code remember that
LDT and other horrors are only used in user space. */
if (seg & (1<<2)) {
/* Must lock the LDT while reading it. */
mutex_lock(&current->mm->context.lock);
desc = current->mm->context.ldt;
desc = (void *)desc + (seg & ~7);
} else {
/* Must disable preemption while reading the GDT. */
desc = (u32 *)get_cpu_gdt_table(get_cpu());
desc = (void *)desc + (seg & ~7);
}

/* Decode the code segment base from the descriptor */
base = get_desc_base((struct desc_struct *)desc);

if (seg & (1<<2))
mutex_unlock(&current->mm->context.lock);
else
put_cpu();

/* Adjust EIP and segment limit, and clamp at the kernel limit.
It's legitimate for segments to wrap at 0xffffffff. */
seg_limit += base;
if (seg_limit < *eip_limit && seg_limit >= base)
*eip_limit = seg_limit;
return ip + base;
}
#endif

#ifdef CONFIG_X86_32
static
#endif
unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *regs)
{
unsigned long addr, seg;
Expand Down
15 changes: 2 additions & 13 deletions arch/x86/mm/fault_32.c
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Original file line number Diff line number Diff line change
Expand Up @@ -81,7 +81,6 @@ static int is_prefetch(struct pt_regs *regs, unsigned long addr,
unsigned char *max_instr;

#ifdef CONFIG_X86_32
unsigned long limit;
if (unlikely(boot_cpu_data.x86_vendor == X86_VENDOR_AMD &&
boot_cpu_data.x86 >= 6)) {
/* Catch an obscure case of prefetch inside an NX page. */
Expand All @@ -90,30 +89,23 @@ static int is_prefetch(struct pt_regs *regs, unsigned long addr,
} else {
return 0;
}
instr = (unsigned char *)get_segment_eip(regs, &limit);
#else
/* If it was a exec fault ignore */
if (error_code & PF_INSTR)
return 0;
instr = (unsigned char __user *)convert_ip_to_linear(current, regs);
#endif

instr = (unsigned char *)convert_ip_to_linear(current, regs);
max_instr = instr + 15;

#ifdef CONFIG_X86_64
if (user_mode(regs) && instr >= (unsigned char *)TASK_SIZE)
return 0;
#endif

while (scan_more && instr < max_instr) {
unsigned char opcode;
unsigned char instr_hi;
unsigned char instr_lo;

#ifdef CONFIG_X86_32
if (instr > (unsigned char *)limit)
break;
#endif
if (probe_kernel_address(instr, opcode))
break;

Expand Down Expand Up @@ -155,10 +147,7 @@ static int is_prefetch(struct pt_regs *regs, unsigned long addr,
case 0x00:
/* Prefetch instruction is 0x0F0D or 0x0F18 */
scan_more = 0;
#ifdef CONFIG_X86_32
if (instr > (unsigned char *)limit)
break;
#endif

if (probe_kernel_address(instr, opcode))
break;
prefetch = (instr_lo == 0xF) &&
Expand Down
15 changes: 2 additions & 13 deletions arch/x86/mm/fault_64.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -84,7 +84,6 @@ static int is_prefetch(struct pt_regs *regs, unsigned long addr,
unsigned char *max_instr;

#ifdef CONFIG_X86_32
unsigned long limit;
if (unlikely(boot_cpu_data.x86_vendor == X86_VENDOR_AMD &&
boot_cpu_data.x86 >= 6)) {
/* Catch an obscure case of prefetch inside an NX page. */
Expand All @@ -93,30 +92,23 @@ static int is_prefetch(struct pt_regs *regs, unsigned long addr,
} else {
return 0;
}
instr = (unsigned char *)get_segment_eip(regs, &limit);
#else
/* If it was a exec fault ignore */
if (error_code & PF_INSTR)
return 0;
instr = (unsigned char __user *)convert_ip_to_linear(current, regs);
#endif

instr = (unsigned char *)convert_ip_to_linear(current, regs);
max_instr = instr + 15;

#ifdef CONFIG_X86_64
if (user_mode(regs) && instr >= (unsigned char *)TASK_SIZE)
return 0;
#endif

while (scan_more && instr < max_instr) {
unsigned char opcode;
unsigned char instr_hi;
unsigned char instr_lo;

#ifdef CONFIG_X86_32
if (instr > (unsigned char *)limit)
break;
#endif
if (probe_kernel_address(instr, opcode))
break;

Expand Down Expand Up @@ -158,10 +150,7 @@ static int is_prefetch(struct pt_regs *regs, unsigned long addr,
case 0x00:
/* Prefetch instruction is 0x0F0D or 0x0F18 */
scan_more = 0;
#ifdef CONFIG_X86_32
if (instr > (unsigned char *)limit)
break;
#endif

if (probe_kernel_address(instr, opcode))
break;
prefetch = (instr_lo == 0xF) &&
Expand Down
6 changes: 4 additions & 2 deletions include/asm-x86/ptrace.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -70,6 +70,10 @@ struct pt_regs {
#include <asm/segment.h>

struct task_struct;

extern unsigned long
convert_ip_to_linear(struct task_struct *child, struct pt_regs *regs);

extern void send_sigtrap(struct task_struct *tsk, struct pt_regs *regs, int error_code);

/*
Expand Down Expand Up @@ -184,8 +188,6 @@ convert_ip_to_linear(struct task_struct *child, struct pt_regs *regs);

#ifdef __KERNEL__

unsigned long get_segment_eip(struct pt_regs *regs, unsigned long *eip_limit);

/*
* These are defined as per linux/ptrace.h, which see.
*/
Expand Down

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