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Subject[PATCH 2/5] powerpc: ftrace, fix cast aliasing and add code verification
From: Steven Rostedt <srostedt@redhat.com>

Impact: clean up and robustness addition

This patch addresses the comments made by Paul Mackerras.
It removes the type casting between unsigned int and unsigned char
pointers, and replaces them with a use of all unsigned int.

Verification that the jump is indeed made to a trampoline has also
been added.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
---
arch/powerpc/kernel/ftrace.c | 121 ++++++++++++++++++++++-------------------
1 files changed, 65 insertions(+), 56 deletions(-)
diff --git a/arch/powerpc/kernel/ftrace.c b/arch/powerpc/kernel/ftrace.c
index 3271cd6..ea454a0 100644
--- a/arch/powerpc/kernel/ftrace.c
+++ b/arch/powerpc/kernel/ftrace.c
@@ -162,26 +162,25 @@ static int
__ftrace_make_nop(struct module *mod,
struct dyn_ftrace *rec, unsigned long addr)
{
- unsigned char replaced[MCOUNT_INSN_SIZE * 2];
- unsigned int *op = (unsigned *)&replaced;
- unsigned char jmp[8];
- unsigned long *ptr = (unsigned long *)&jmp;
+ unsigned int op;
+ unsigned int jmp[5];
+ unsigned long ptr;
unsigned long ip = rec->ip;
unsigned long tramp;
int offset;

/* read where this goes */
- if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
+ if (probe_kernel_read(&op, (void *)ip, sizeof(int)))
return -EFAULT;

/* Make sure that that this is still a 24bit jump */
- if (!is_bl_op(*op)) {
- printk(KERN_ERR "Not expected bl: opcode is %x\n", *op);
+ if (!is_bl_op(op)) {
+ printk(KERN_ERR "Not expected bl: opcode is %x\n", op);
return -EINVAL;
}

/* lets find where the pointer goes */
- tramp = find_bl_target(ip, *op);
+ tramp = find_bl_target(ip, op);

/*
* On PPC64 the trampoline looks like:
@@ -200,19 +199,25 @@ __ftrace_make_nop(struct module *mod,
DEBUGP("ip:%lx jumps to %lx r2: %lx", ip, tramp, mod->arch.toc);

/* Find where the trampoline jumps to */
- if (probe_kernel_read(jmp, (void *)tramp, 8)) {
+ if (probe_kernel_read(jmp, (void *)tramp, sizeof(jmp))) {
printk(KERN_ERR "Failed to read %lx\n", tramp);
return -EFAULT;
}

- DEBUGP(" %08x %08x",
- (unsigned)(*ptr >> 32),
- (unsigned)*ptr);
+ DEBUGP(" %08x %08x", jmp[0], jmp[1]);
+
+ /* verify that this is what we expect it to be */
+ if (((jmp[0] & 0xffff0000) != 0x3d820000) ||
+ ((jmp[1] & 0xffff0000) != 0x398c0000) ||
+ (jmp[2] != 0xf8410028) ||
+ (jmp[3] != 0xe96c0020) ||
+ (jmp[4] != 0xe84c0028)) {
+ printk(KERN_ERR "Not a trampoline\n");
+ return -EINVAL;
+ }

- offset = (unsigned)jmp[2] << 24 |
- (unsigned)jmp[3] << 16 |
- (unsigned)jmp[6] << 8 |
- (unsigned)jmp[7];
+ offset = (unsigned)((unsigned short)jmp[0]) << 16 |
+ (unsigned)((unsigned short)jmp[1]);

DEBUGP(" %x ", offset);

@@ -225,13 +230,13 @@ __ftrace_make_nop(struct module *mod,
return -EFAULT;
}

- DEBUGP(" %08x %08x\n",
- (unsigned)(*ptr >> 32),
- (unsigned)*ptr);
+ DEBUGP(" %08x %08x\n", jmp[0], jmp[1]);
+
+ ptr = ((unsigned long)jmp[0] << 32) + jmp[1];

/* This should match what was called */
- if (*ptr != GET_ADDR(addr)) {
- printk(KERN_ERR "addr does not match %lx\n", *ptr);
+ if (ptr != GET_ADDR(addr)) {
+ printk(KERN_ERR "addr does not match %lx\n", ptr);
return -EINVAL;
}

@@ -240,11 +245,11 @@ __ftrace_make_nop(struct module *mod,
* 0xe8, 0x41, 0x00, 0x28 ld r2,40(r1)
* This needs to be turned to a nop too.
*/
- if (probe_kernel_read(replaced, (void *)(ip+4), MCOUNT_INSN_SIZE))
+ if (probe_kernel_read(&op, (void *)(ip+4), MCOUNT_INSN_SIZE))
return -EFAULT;

- if (*op != 0xe8410028) {
- printk(KERN_ERR "Next line is not ld! (%08x)\n", *op);
+ if (op != 0xe8410028) {
+ printk(KERN_ERR "Next line is not ld! (%08x)\n", op);
return -EINVAL;
}

@@ -261,9 +266,9 @@ __ftrace_make_nop(struct module *mod,
* ld r2,40(r1)
* 1:
*/
- op[0] = 0x48000008; /* b +8 */
+ op = 0x48000008; /* b +8 */

- if (probe_kernel_write((void *)ip, replaced, MCOUNT_INSN_SIZE))
+ if (probe_kernel_write((void *)ip, &op, MCOUNT_INSN_SIZE))
return -EPERM;

return 0;
@@ -274,46 +279,52 @@ static int
__ftrace_make_nop(struct module *mod,
struct dyn_ftrace *rec, unsigned long addr)
{
- unsigned char replaced[MCOUNT_INSN_SIZE];
- unsigned int *op = (unsigned *)&replaced;
- unsigned char jmp[8];
- unsigned int *ptr = (unsigned int *)&jmp;
+ unsigned int op;
+ unsigned int jmp[4];
unsigned long ip = rec->ip;
unsigned long tramp;
- int offset;

- if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
+ if (probe_kernel_read(&op, (void *)ip, MCOUNT_INSN_SIZE))
return -EFAULT;

/* Make sure that that this is still a 24bit jump */
- if (!is_bl_op(*op)) {
- printk(KERN_ERR "Not expected bl: opcode is %x\n", *op);
+ if (!is_bl_op(op)) {
+ printk(KERN_ERR "Not expected bl: opcode is %x\n", op);
return -EINVAL;
}

/* lets find where the pointer goes */
- tramp = find_bl_target(ip, *op);
+ tramp = find_bl_target(ip, op);

/*
* On PPC32 the trampoline looks like:
- * lis r11,sym@ha
- * addi r11,r11,sym@l
- * mtctr r11
- * bctr
+ * 0x3d, 0x60, 0x00, 0x00 lis r11,sym@ha
+ * 0x39, 0x6b, 0x00, 0x00 addi r11,r11,sym@l
+ * 0x7d, 0x69, 0x03, 0xa6 mtctr r11
+ * 0x4e, 0x80, 0x04, 0x20 bctr
*/

DEBUGP("ip:%lx jumps to %lx", ip, tramp);

/* Find where the trampoline jumps to */
- if (probe_kernel_read(jmp, (void *)tramp, 8)) {
+ if (probe_kernel_read(jmp, (void *)tramp, sizeof(jmp))) {
printk(KERN_ERR "Failed to read %lx\n", tramp);
return -EFAULT;
}

- DEBUGP(" %08x %08x ", ptr[0], ptr[1]);
+ DEBUGP(" %08x %08x ", jmp[0], jmp[1]);
+
+ /* verify that this is what we expect it to be */
+ if (((jmp[0] & 0xffff0000) != 0x3d600000) ||
+ ((jmp[1] & 0xffff0000) != 0x396b0000) ||
+ (jmp[2] != 0x7d6903a6) ||
+ (jmp[3] != 0x4e800420)) {
+ printk(KERN_ERR "Not a trampoline\n");
+ return -EINVAL;
+ }

- tramp = (ptr[1] & 0xffff) |
- ((ptr[0] & 0xffff) << 16);
+ tramp = (jmp[1] & 0xffff) |
+ ((jmp[0] & 0xffff) << 16);
if (tramp & 0x8000)
tramp -= 0x10000;

@@ -326,9 +337,9 @@ __ftrace_make_nop(struct module *mod,
return -EINVAL;
}

- op[0] = PPC_NOP_INSTR;
+ op = PPC_NOP_INSTR;

- if (probe_kernel_write((void *)ip, replaced, MCOUNT_INSN_SIZE))
+ if (probe_kernel_write((void *)ip, &op, MCOUNT_INSN_SIZE))
return -EPERM;

return 0;
@@ -384,13 +395,12 @@ int ftrace_make_nop(struct module *mod,
static int
__ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
- unsigned char replaced[MCOUNT_INSN_SIZE * 2];
- unsigned int *op = (unsigned *)&replaced;
+ unsigned int op[2];
unsigned long ip = rec->ip;
unsigned long offset;

/* read where this goes */
- if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE * 2))
+ if (probe_kernel_read(op, (void *)ip, MCOUNT_INSN_SIZE * 2))
return -EFAULT;

/*
@@ -425,7 +435,7 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)

DEBUGP("write to %lx\n", rec->ip);

- if (probe_kernel_write((void *)ip, replaced, MCOUNT_INSN_SIZE * 2))
+ if (probe_kernel_write((void *)ip, op, MCOUNT_INSN_SIZE * 2))
return -EPERM;

return 0;
@@ -434,18 +444,17 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
static int
__ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
{
- unsigned char replaced[MCOUNT_INSN_SIZE];
- unsigned int *op = (unsigned *)&replaced;
+ unsigned int op;
unsigned long ip = rec->ip;
unsigned long offset;

/* read where this goes */
- if (probe_kernel_read(replaced, (void *)ip, MCOUNT_INSN_SIZE))
+ if (probe_kernel_read(&op, (void *)ip, MCOUNT_INSN_SIZE))
return -EFAULT;

/* It should be pointing to a nop */
- if (op[0] != PPC_NOP_INSTR) {
- printk(KERN_ERR "Expected NOP but have %x\n", op[0]);
+ if (op != PPC_NOP_INSTR) {
+ printk(KERN_ERR "Expected NOP but have %x\n", op);
return -EINVAL;
}

@@ -465,11 +474,11 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
}

/* Set to "bl addr" */
- op[0] = branch_offset(offset);
+ op = branch_offset(offset);

DEBUGP("write to %lx\n", rec->ip);

- if (probe_kernel_write((void *)ip, replaced, MCOUNT_INSN_SIZE))
+ if (probe_kernel_write((void *)ip, &op, MCOUNT_INSN_SIZE))
return -EPERM;

return 0;
--
1.5.6.5
--


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