Skip to content

Commit ab0615e

Browse files
vitkyrkakees
vitkyrka
authored and
kees
committed
arm: use fixmap for text patching when text is RO
Use fixmaps for text patching when the kernel text is read-only, inspired by x86. This makes jump labels and kprobes work with the currently available CONFIG_DEBUG_SET_MODULE_RONX and the upcoming CONFIG_DEBUG_RODATA options. Signed-off-by: Rabin Vincent <rabin@rab.in> [kees: fixed up for merge with "arm: use generic fixmap.h"] [kees: added parse acquire/release annotations to pass C=1 builds] [kees: always use stop_machine to keep TLB flushing local] Signed-off-by: Kees Cook <keescook@chromium.org> Acked-by: Nicolas Pitre <nico@linaro.org>
1 parent 99b4ac9 commit ab0615e

File tree

4 files changed

+89
-21
lines changed

4 files changed

+89
-21
lines changed

‎arch/arm/include/asm/fixmap.h

Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -11,6 +11,10 @@ enum fixed_addresses {
1111
FIX_KMAP_BEGIN,
1212
FIX_KMAP_END = FIX_KMAP_BEGIN + (KM_TYPE_NR * NR_CPUS) - 1,
1313

14+
/* Support writing RO kernel text via kprobes, jump labels, etc. */
15+
FIX_TEXT_POKE0,
16+
FIX_TEXT_POKE1,
17+
1418
__end_of_fixed_addresses
1519
};
1620

‎arch/arm/kernel/jump_label.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -19,7 +19,7 @@ static void __arch_jump_label_transform(struct jump_entry *entry,
1919
insn = arm_gen_nop();
2020

2121
if (is_static)
22-
__patch_text(addr, insn);
22+
__patch_text_early(addr, insn);
2323
else
2424
patch_text(addr, insn);
2525
}

‎arch/arm/kernel/patch.c

Lines changed: 73 additions & 19 deletions
Original file line numberDiff line numberDiff line change
@@ -1,8 +1,11 @@
11
#include <linux/kernel.h>
2+
#include <linux/spinlock.h>
23
#include <linux/kprobes.h>
4+
#include <linux/mm.h>
35
#include <linux/stop_machine.h>
46

57
#include <asm/cacheflush.h>
8+
#include <asm/fixmap.h>
69
#include <asm/smp_plat.h>
710
#include <asm/opcodes.h>
811

@@ -13,21 +16,77 @@ struct patch {
1316
unsigned int insn;
1417
};
1518

16-
void __kprobes __patch_text(void *addr, unsigned int insn)
19+
static DEFINE_SPINLOCK(patch_lock);
20+
21+
static void __kprobes *patch_map(void *addr, int fixmap, unsigned long *flags)
22+
__acquires(&patch_lock)
23+
{
24+
unsigned int uintaddr = (uintptr_t) addr;
25+
bool module = !core_kernel_text(uintaddr);
26+
struct page *page;
27+
28+
if (module && IS_ENABLED(CONFIG_DEBUG_SET_MODULE_RONX))
29+
page = vmalloc_to_page(addr);
30+
else if (!module && IS_ENABLED(CONFIG_DEBUG_RODATA))
31+
page = virt_to_page(addr);
32+
else
33+
return addr;
34+
35+
if (flags)
36+
spin_lock_irqsave(&patch_lock, *flags);
37+
else
38+
__acquire(&patch_lock);
39+
40+
set_fixmap(fixmap, page_to_phys(page));
41+
42+
return (void *) (__fix_to_virt(fixmap) + (uintaddr & ~PAGE_MASK));
43+
}
44+
45+
static void __kprobes patch_unmap(int fixmap, unsigned long *flags)
46+
__releases(&patch_lock)
47+
{
48+
clear_fixmap(fixmap);
49+
50+
if (flags)
51+
spin_unlock_irqrestore(&patch_lock, *flags);
52+
else
53+
__release(&patch_lock);
54+
}
55+
56+
void __kprobes __patch_text_real(void *addr, unsigned int insn, bool remap)
1757
{
1858
bool thumb2 = IS_ENABLED(CONFIG_THUMB2_KERNEL);
59+
unsigned int uintaddr = (uintptr_t) addr;
60+
bool twopage = false;
61+
unsigned long flags;
62+
void *waddr = addr;
1963
int size;
2064

65+
if (remap)
66+
waddr = patch_map(addr, FIX_TEXT_POKE0, &flags);
67+
else
68+
__acquire(&patch_lock);
69+
2170
if (thumb2 && __opcode_is_thumb16(insn)) {
22-
*(u16 *)addr = __opcode_to_mem_thumb16(insn);
71+
*(u16 *)waddr = __opcode_to_mem_thumb16(insn);
2372
size = sizeof(u16);
24-
} else if (thumb2 && ((uintptr_t)addr & 2)) {
73+
} else if (thumb2 && (uintaddr & 2)) {
2574
u16 first = __opcode_thumb32_first(insn);
2675
u16 second = __opcode_thumb32_second(insn);
27-
u16 *addrh = addr;
76+
u16 *addrh0 = waddr;
77+
u16 *addrh1 = waddr + 2;
78+
79+
twopage = (uintaddr & ~PAGE_MASK) == PAGE_SIZE - 2;
80+
if (twopage && remap)
81+
addrh1 = patch_map(addr + 2, FIX_TEXT_POKE1, NULL);
82+
83+
*addrh0 = __opcode_to_mem_thumb16(first);
84+
*addrh1 = __opcode_to_mem_thumb16(second);
2885

29-
addrh[0] = __opcode_to_mem_thumb16(first);
30-
addrh[1] = __opcode_to_mem_thumb16(second);
86+
if (twopage && addrh1 != addr + 2) {
87+
flush_kernel_vmap_range(addrh1, 2);
88+
patch_unmap(FIX_TEXT_POKE1, NULL);
89+
}
3190

3291
size = sizeof(u32);
3392
} else {
@@ -36,10 +95,16 @@ void __kprobes __patch_text(void *addr, unsigned int insn)
3695
else
3796
insn = __opcode_to_mem_arm(insn);
3897

39-
*(u32 *)addr = insn;
98+
*(u32 *)waddr = insn;
4099
size = sizeof(u32);
41100
}
42101

102+
if (waddr != addr) {
103+
flush_kernel_vmap_range(waddr, twopage ? size / 2 : size);
104+
patch_unmap(FIX_TEXT_POKE0, &flags);
105+
} else
106+
__release(&patch_lock);
107+
43108
flush_icache_range((uintptr_t)(addr),
44109
(uintptr_t)(addr) + size);
45110
}
@@ -60,16 +125,5 @@ void __kprobes patch_text(void *addr, unsigned int insn)
60125
.insn = insn,
61126
};
62127

63-
if (cache_ops_need_broadcast()) {
64-
stop_machine(patch_text_stop_machine, &patch, cpu_online_mask);
65-
} else {
66-
bool straddles_word = IS_ENABLED(CONFIG_THUMB2_KERNEL)
67-
&& __opcode_is_thumb32(insn)
68-
&& ((uintptr_t)addr & 2);
69-
70-
if (straddles_word)
71-
stop_machine(patch_text_stop_machine, &patch, NULL);
72-
else
73-
__patch_text(addr, insn);
74-
}
128+
stop_machine(patch_text_stop_machine, &patch, NULL);
75129
}

‎arch/arm/kernel/patch.h

Lines changed: 11 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -2,6 +2,16 @@
22
#define _ARM_KERNEL_PATCH_H
33

44
void patch_text(void *addr, unsigned int insn);
5-
void __patch_text(void *addr, unsigned int insn);
5+
void __patch_text_real(void *addr, unsigned int insn, bool remap);
6+
7+
static inline void __patch_text(void *addr, unsigned int insn)
8+
{
9+
__patch_text_real(addr, insn, true);
10+
}
11+
12+
static inline void __patch_text_early(void *addr, unsigned int insn)
13+
{
14+
__patch_text_real(addr, insn, false);
15+
}
616

717
#endif

0 commit comments

Comments
 (0)