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linux/arch/powerpc/lib/code-patching.c
Anju T 51c9c08439 powerpc/kprobes: Implement Optprobes 
Current infrastructure of kprobe uses the unconditional trap instruction
to probe a running kernel. Optprobe allows kprobe to replace the trap
with a branch instruction to a detour buffer. Detour buffer contains
instructions to create an in memory pt_regs. Detour buffer also has a
call to optimized_callback() which in turn call the pre_handler(). After
the execution of the pre-handler, a call is made for instruction
emulation. The NIP is determined in advanced through dummy instruction
emulation and a branch instruction is created to the NIP at the end of
the trampoline.

To address the limitation of branch instruction in POWER architecture,
detour buffer slot is allocated from a reserved area. For the time
being, 64KB is reserved in memory for this purpose.

Instructions which can be emulated using analyse_instr() are the
candidates for optimization. Before optimization ensure that the address
range between the detour buffer allocated and the instruction being
probed is within +/- 32MB.

Signed-off-by: Anju T Sudhakar <anju@linux.vnet.ibm.com>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
2017-02-10 13:28:04 +11:00

514 lines
14 KiB
C
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/*
* Copyright 2008 Michael Ellerman, IBM Corporation.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*/
#include <linux/kernel.h>
#include <linux/vmalloc.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <asm/page.h>
#include <asm/code-patching.h>
#include <linux/uaccess.h>
int patch_instruction(unsigned int *addr, unsigned int instr)
{
int err;
__put_user_size(instr, addr, 4, err);
if (err)
return err;
asm ("dcbst 0, %0; sync; icbi 0,%0; sync; isync" : : "r" (addr));
return 0;
}
int patch_branch(unsigned int *addr, unsigned long target, int flags)
{
return patch_instruction(addr, create_branch(addr, target, flags));
}
bool is_offset_in_branch_range(long offset)
{
/*
* Powerpc branch instruction is :
*
* 0 6 30 31
* +---------+----------------+---+---+
* | opcode | LI |AA |LK |
* +---------+----------------+---+---+
* Where AA = 0 and LK = 0
*
* LI is a signed 24 bits integer. The real branch offset is computed
* by: imm32 = SignExtend(LI:'0b00', 32);
*
* So the maximum forward branch should be:
* (0x007fffff << 2) = 0x01fffffc = 0x1fffffc
* The maximum backward branch should be:
* (0xff800000 << 2) = 0xfe000000 = -0x2000000
*/
return (offset >= -0x2000000 && offset <= 0x1fffffc && !(offset & 0x3));
}
/*
* Helper to check if a given instruction is a conditional branch
* Derived from the conditional checks in analyse_instr()
*/
bool __kprobes is_conditional_branch(unsigned int instr)
{
unsigned int opcode = instr >> 26;
if (opcode == 16) /* bc, bca, bcl, bcla */
return true;
if (opcode == 19) {
switch ((instr >> 1) & 0x3ff) {
case 16: /* bclr, bclrl */
case 528: /* bcctr, bcctrl */
case 560: /* bctar, bctarl */
return true;
}
}
return false;
}
unsigned int create_branch(const unsigned int *addr,
unsigned long target, int flags)
{
unsigned int instruction;
long offset;
offset = target;
if (! (flags & BRANCH_ABSOLUTE))
offset = offset - (unsigned long)addr;
/* Check we can represent the target in the instruction format */
if (!is_offset_in_branch_range(offset))
return 0;
/* Mask out the flags and target, so they don't step on each other. */
instruction = 0x48000000 | (flags & 0x3) | (offset & 0x03FFFFFC);
return instruction;
}
unsigned int create_cond_branch(const unsigned int *addr,
unsigned long target, int flags)
{
unsigned int instruction;
long offset;
offset = target;
if (! (flags & BRANCH_ABSOLUTE))
offset = offset - (unsigned long)addr;
/* Check we can represent the target in the instruction format */
if (offset < -0x8000 || offset > 0x7FFF || offset & 0x3)
return 0;
/* Mask out the flags and target, so they don't step on each other. */
instruction = 0x40000000 | (flags & 0x3FF0003) | (offset & 0xFFFC);
return instruction;
}
static unsigned int branch_opcode(unsigned int instr)
{
return (instr >> 26) & 0x3F;
}
static int instr_is_branch_iform(unsigned int instr)
{
return branch_opcode(instr) == 18;
}
static int instr_is_branch_bform(unsigned int instr)
{
return branch_opcode(instr) == 16;
}
int instr_is_relative_branch(unsigned int instr)
{
if (instr & BRANCH_ABSOLUTE)
return 0;
return instr_is_branch_iform(instr) || instr_is_branch_bform(instr);
}
static unsigned long branch_iform_target(const unsigned int *instr)
{
signed long imm;
imm = *instr & 0x3FFFFFC;
/* If the top bit of the immediate value is set this is negative */
if (imm & 0x2000000)
imm -= 0x4000000;
if ((*instr & BRANCH_ABSOLUTE) == 0)
imm += (unsigned long)instr;
return (unsigned long)imm;
}
static unsigned long branch_bform_target(const unsigned int *instr)
{
signed long imm;
imm = *instr & 0xFFFC;
/* If the top bit of the immediate value is set this is negative */
if (imm & 0x8000)
imm -= 0x10000;
if ((*instr & BRANCH_ABSOLUTE) == 0)
imm += (unsigned long)instr;
return (unsigned long)imm;
}
unsigned long branch_target(const unsigned int *instr)
{
if (instr_is_branch_iform(*instr))
return branch_iform_target(instr);
else if (instr_is_branch_bform(*instr))
return branch_bform_target(instr);
return 0;
}
int instr_is_branch_to_addr(const unsigned int *instr, unsigned long addr)
{
if (instr_is_branch_iform(*instr) || instr_is_branch_bform(*instr))
return branch_target(instr) == addr;
return 0;
}
unsigned int translate_branch(const unsigned int *dest, const unsigned int *src)
{
unsigned long target;
target = branch_target(src);
if (instr_is_branch_iform(*src))
return create_branch(dest, target, *src);
else if (instr_is_branch_bform(*src))
return create_cond_branch(dest, target, *src);
return 0;
}
#ifdef CONFIG_PPC_BOOK3E_64
void __patch_exception(int exc, unsigned long addr)
{
extern unsigned int interrupt_base_book3e;
unsigned int *ibase = &interrupt_base_book3e;
/* Our exceptions vectors start with a NOP and -then- a branch
* to deal with single stepping from userspace which stops on
* the second instruction. Thus we need to patch the second
* instruction of the exception, not the first one
*/
patch_branch(ibase + (exc / 4) + 1, addr, 0);
}
#endif
#ifdef CONFIG_CODE_PATCHING_SELFTEST
static void __init test_trampoline(void)
{
asm ("nop;\n");
}
#define check(x) \
if (!(x)) printk("code-patching: test failed at line %d\n", __LINE__);
static void __init test_branch_iform(void)
{
unsigned int instr;
unsigned long addr;
addr = (unsigned long)&instr;
/* The simplest case, branch to self, no flags */
check(instr_is_branch_iform(0x48000000));
/* All bits of target set, and flags */
check(instr_is_branch_iform(0x4bffffff));
/* High bit of opcode set, which is wrong */
check(!instr_is_branch_iform(0xcbffffff));
/* Middle bits of opcode set, which is wrong */
check(!instr_is_branch_iform(0x7bffffff));
/* Simplest case, branch to self with link */
check(instr_is_branch_iform(0x48000001));
/* All bits of targets set */
check(instr_is_branch_iform(0x4bfffffd));
/* Some bits of targets set */
check(instr_is_branch_iform(0x4bff00fd));
/* Must be a valid branch to start with */
check(!instr_is_branch_iform(0x7bfffffd));
/* Absolute branch to 0x100 */
instr = 0x48000103;
check(instr_is_branch_to_addr(&instr, 0x100));
/* Absolute branch to 0x420fc */
instr = 0x480420ff;
check(instr_is_branch_to_addr(&instr, 0x420fc));
/* Maximum positive relative branch, + 20MB - 4B */
instr = 0x49fffffc;
check(instr_is_branch_to_addr(&instr, addr + 0x1FFFFFC));
/* Smallest negative relative branch, - 4B */
instr = 0x4bfffffc;
check(instr_is_branch_to_addr(&instr, addr - 4));
/* Largest negative relative branch, - 32 MB */
instr = 0x4a000000;
check(instr_is_branch_to_addr(&instr, addr - 0x2000000));
/* Branch to self, with link */
instr = create_branch(&instr, addr, BRANCH_SET_LINK);
check(instr_is_branch_to_addr(&instr, addr));
/* Branch to self - 0x100, with link */
instr = create_branch(&instr, addr - 0x100, BRANCH_SET_LINK);
check(instr_is_branch_to_addr(&instr, addr - 0x100));
/* Branch to self + 0x100, no link */
instr = create_branch(&instr, addr + 0x100, 0);
check(instr_is_branch_to_addr(&instr, addr + 0x100));
/* Maximum relative negative offset, - 32 MB */
instr = create_branch(&instr, addr - 0x2000000, BRANCH_SET_LINK);
check(instr_is_branch_to_addr(&instr, addr - 0x2000000));
/* Out of range relative negative offset, - 32 MB + 4*/
instr = create_branch(&instr, addr - 0x2000004, BRANCH_SET_LINK);
check(instr == 0);
/* Out of range relative positive offset, + 32 MB */
instr = create_branch(&instr, addr + 0x2000000, BRANCH_SET_LINK);
check(instr == 0);
/* Unaligned target */
instr = create_branch(&instr, addr + 3, BRANCH_SET_LINK);
check(instr == 0);
/* Check flags are masked correctly */
instr = create_branch(&instr, addr, 0xFFFFFFFC);
check(instr_is_branch_to_addr(&instr, addr));
check(instr == 0x48000000);
}
static void __init test_create_function_call(void)
{
unsigned int *iptr;
unsigned long dest;
/* Check we can create a function call */
iptr = (unsigned int *)ppc_function_entry(test_trampoline);
dest = ppc_function_entry(test_create_function_call);
patch_instruction(iptr, create_branch(iptr, dest, BRANCH_SET_LINK));
check(instr_is_branch_to_addr(iptr, dest));
}
static void __init test_branch_bform(void)
{
unsigned long addr;
unsigned int *iptr, instr, flags;
iptr = &instr;
addr = (unsigned long)iptr;
/* The simplest case, branch to self, no flags */
check(instr_is_branch_bform(0x40000000));
/* All bits of target set, and flags */
check(instr_is_branch_bform(0x43ffffff));
/* High bit of opcode set, which is wrong */
check(!instr_is_branch_bform(0xc3ffffff));
/* Middle bits of opcode set, which is wrong */
check(!instr_is_branch_bform(0x7bffffff));
/* Absolute conditional branch to 0x100 */
instr = 0x43ff0103;
check(instr_is_branch_to_addr(&instr, 0x100));
/* Absolute conditional branch to 0x20fc */
instr = 0x43ff20ff;
check(instr_is_branch_to_addr(&instr, 0x20fc));
/* Maximum positive relative conditional branch, + 32 KB - 4B */
instr = 0x43ff7ffc;
check(instr_is_branch_to_addr(&instr, addr + 0x7FFC));
/* Smallest negative relative conditional branch, - 4B */
instr = 0x43fffffc;
check(instr_is_branch_to_addr(&instr, addr - 4));
/* Largest negative relative conditional branch, - 32 KB */
instr = 0x43ff8000;
check(instr_is_branch_to_addr(&instr, addr - 0x8000));
/* All condition code bits set & link */
flags = 0x3ff000 | BRANCH_SET_LINK;
/* Branch to self */
instr = create_cond_branch(iptr, addr, flags);
check(instr_is_branch_to_addr(&instr, addr));
/* Branch to self - 0x100 */
instr = create_cond_branch(iptr, addr - 0x100, flags);
check(instr_is_branch_to_addr(&instr, addr - 0x100));
/* Branch to self + 0x100 */
instr = create_cond_branch(iptr, addr + 0x100, flags);
check(instr_is_branch_to_addr(&instr, addr + 0x100));
/* Maximum relative negative offset, - 32 KB */
instr = create_cond_branch(iptr, addr - 0x8000, flags);
check(instr_is_branch_to_addr(&instr, addr - 0x8000));
/* Out of range relative negative offset, - 32 KB + 4*/
instr = create_cond_branch(iptr, addr - 0x8004, flags);
check(instr == 0);
/* Out of range relative positive offset, + 32 KB */
instr = create_cond_branch(iptr, addr + 0x8000, flags);
check(instr == 0);
/* Unaligned target */
instr = create_cond_branch(iptr, addr + 3, flags);
check(instr == 0);
/* Check flags are masked correctly */
instr = create_cond_branch(iptr, addr, 0xFFFFFFFC);
check(instr_is_branch_to_addr(&instr, addr));
check(instr == 0x43FF0000);
}
static void __init test_translate_branch(void)
{
unsigned long addr;
unsigned int *p, *q;
void *buf;
buf = vmalloc(PAGE_ALIGN(0x2000000 + 1));
check(buf);
if (!buf)
return;
/* Simple case, branch to self moved a little */
p = buf;
addr = (unsigned long)p;
patch_branch(p, addr, 0);
check(instr_is_branch_to_addr(p, addr));
q = p + 1;
patch_instruction(q, translate_branch(q, p));
check(instr_is_branch_to_addr(q, addr));
/* Maximum negative case, move b . to addr + 32 MB */
p = buf;
addr = (unsigned long)p;
patch_branch(p, addr, 0);
q = buf + 0x2000000;
patch_instruction(q, translate_branch(q, p));
check(instr_is_branch_to_addr(p, addr));
check(instr_is_branch_to_addr(q, addr));
check(*q == 0x4a000000);
/* Maximum positive case, move x to x - 32 MB + 4 */
p = buf + 0x2000000;
addr = (unsigned long)p;
patch_branch(p, addr, 0);
q = buf + 4;
patch_instruction(q, translate_branch(q, p));
check(instr_is_branch_to_addr(p, addr));
check(instr_is_branch_to_addr(q, addr));
check(*q == 0x49fffffc);
/* Jump to x + 16 MB moved to x + 20 MB */
p = buf;
addr = 0x1000000 + (unsigned long)buf;
patch_branch(p, addr, BRANCH_SET_LINK);
q = buf + 0x1400000;
patch_instruction(q, translate_branch(q, p));
check(instr_is_branch_to_addr(p, addr));
check(instr_is_branch_to_addr(q, addr));
/* Jump to x + 16 MB moved to x - 16 MB + 4 */
p = buf + 0x1000000;
addr = 0x2000000 + (unsigned long)buf;
patch_branch(p, addr, 0);
q = buf + 4;
patch_instruction(q, translate_branch(q, p));
check(instr_is_branch_to_addr(p, addr));
check(instr_is_branch_to_addr(q, addr));
/* Conditional branch tests */
/* Simple case, branch to self moved a little */
p = buf;
addr = (unsigned long)p;
patch_instruction(p, create_cond_branch(p, addr, 0));
check(instr_is_branch_to_addr(p, addr));
q = p + 1;
patch_instruction(q, translate_branch(q, p));
check(instr_is_branch_to_addr(q, addr));
/* Maximum negative case, move b . to addr + 32 KB */
p = buf;
addr = (unsigned long)p;
patch_instruction(p, create_cond_branch(p, addr, 0xFFFFFFFC));
q = buf + 0x8000;
patch_instruction(q, translate_branch(q, p));
check(instr_is_branch_to_addr(p, addr));
check(instr_is_branch_to_addr(q, addr));
check(*q == 0x43ff8000);
/* Maximum positive case, move x to x - 32 KB + 4 */
p = buf + 0x8000;
addr = (unsigned long)p;
patch_instruction(p, create_cond_branch(p, addr, 0xFFFFFFFC));
q = buf + 4;
patch_instruction(q, translate_branch(q, p));
check(instr_is_branch_to_addr(p, addr));
check(instr_is_branch_to_addr(q, addr));
check(*q == 0x43ff7ffc);
/* Jump to x + 12 KB moved to x + 20 KB */
p = buf;
addr = 0x3000 + (unsigned long)buf;
patch_instruction(p, create_cond_branch(p, addr, BRANCH_SET_LINK));
q = buf + 0x5000;
patch_instruction(q, translate_branch(q, p));
check(instr_is_branch_to_addr(p, addr));
check(instr_is_branch_to_addr(q, addr));
/* Jump to x + 8 KB moved to x - 8 KB + 4 */
p = buf + 0x2000;
addr = 0x4000 + (unsigned long)buf;
patch_instruction(p, create_cond_branch(p, addr, 0));
q = buf + 4;
patch_instruction(q, translate_branch(q, p));
check(instr_is_branch_to_addr(p, addr));
check(instr_is_branch_to_addr(q, addr));
/* Free the buffer we were using */
vfree(buf);
}
static int __init test_code_patching(void)
{
printk(KERN_DEBUG "Running code patching self-tests ...\n");
test_branch_iform();
test_branch_bform();
test_create_function_call();
test_translate_branch();
return 0;
}
late_initcall(test_code_patching);
#endif /* CONFIG_CODE_PATCHING_SELFTEST */
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