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arm: use fixmap for text patching when text is RO
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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>
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Rabin Vincent authored and Kees Cook committed Oct 16, 2014
1 parent 99b4ac9 commit ab0615e
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Showing 4 changed files with 89 additions and 21 deletions.
4 changes: 4 additions & 0 deletions arch/arm/include/asm/fixmap.h
Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,10 @@ enum fixed_addresses {
FIX_KMAP_BEGIN,
FIX_KMAP_END = FIX_KMAP_BEGIN + (KM_TYPE_NR * NR_CPUS) - 1,

/* Support writing RO kernel text via kprobes, jump labels, etc. */
FIX_TEXT_POKE0,
FIX_TEXT_POKE1,

__end_of_fixed_addresses
};

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2 changes: 1 addition & 1 deletion arch/arm/kernel/jump_label.c
Original file line number Diff line number Diff line change
Expand Up @@ -19,7 +19,7 @@ static void __arch_jump_label_transform(struct jump_entry *entry,
insn = arm_gen_nop();

if (is_static)
__patch_text(addr, insn);
__patch_text_early(addr, insn);
else
patch_text(addr, insn);
}
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92 changes: 73 additions & 19 deletions arch/arm/kernel/patch.c
Original file line number Diff line number Diff line change
@@ -1,8 +1,11 @@
#include <linux/kernel.h>
#include <linux/spinlock.h>
#include <linux/kprobes.h>
#include <linux/mm.h>
#include <linux/stop_machine.h>

#include <asm/cacheflush.h>
#include <asm/fixmap.h>
#include <asm/smp_plat.h>
#include <asm/opcodes.h>

Expand All @@ -13,21 +16,77 @@ struct patch {
unsigned int insn;
};

void __kprobes __patch_text(void *addr, unsigned int insn)
static DEFINE_SPINLOCK(patch_lock);

static void __kprobes *patch_map(void *addr, int fixmap, unsigned long *flags)
__acquires(&patch_lock)
{
unsigned int uintaddr = (uintptr_t) addr;
bool module = !core_kernel_text(uintaddr);
struct page *page;

if (module && IS_ENABLED(CONFIG_DEBUG_SET_MODULE_RONX))
page = vmalloc_to_page(addr);
else if (!module && IS_ENABLED(CONFIG_DEBUG_RODATA))
page = virt_to_page(addr);
else
return addr;

if (flags)
spin_lock_irqsave(&patch_lock, *flags);
else
__acquire(&patch_lock);

set_fixmap(fixmap, page_to_phys(page));

return (void *) (__fix_to_virt(fixmap) + (uintaddr & ~PAGE_MASK));
}

static void __kprobes patch_unmap(int fixmap, unsigned long *flags)
__releases(&patch_lock)
{
clear_fixmap(fixmap);

if (flags)
spin_unlock_irqrestore(&patch_lock, *flags);
else
__release(&patch_lock);
}

void __kprobes __patch_text_real(void *addr, unsigned int insn, bool remap)
{
bool thumb2 = IS_ENABLED(CONFIG_THUMB2_KERNEL);
unsigned int uintaddr = (uintptr_t) addr;
bool twopage = false;
unsigned long flags;
void *waddr = addr;
int size;

if (remap)
waddr = patch_map(addr, FIX_TEXT_POKE0, &flags);
else
__acquire(&patch_lock);

if (thumb2 && __opcode_is_thumb16(insn)) {
*(u16 *)addr = __opcode_to_mem_thumb16(insn);
*(u16 *)waddr = __opcode_to_mem_thumb16(insn);
size = sizeof(u16);
} else if (thumb2 && ((uintptr_t)addr & 2)) {
} else if (thumb2 && (uintaddr & 2)) {
u16 first = __opcode_thumb32_first(insn);
u16 second = __opcode_thumb32_second(insn);
u16 *addrh = addr;
u16 *addrh0 = waddr;
u16 *addrh1 = waddr + 2;

twopage = (uintaddr & ~PAGE_MASK) == PAGE_SIZE - 2;
if (twopage && remap)
addrh1 = patch_map(addr + 2, FIX_TEXT_POKE1, NULL);

*addrh0 = __opcode_to_mem_thumb16(first);
*addrh1 = __opcode_to_mem_thumb16(second);

addrh[0] = __opcode_to_mem_thumb16(first);
addrh[1] = __opcode_to_mem_thumb16(second);
if (twopage && addrh1 != addr + 2) {
flush_kernel_vmap_range(addrh1, 2);
patch_unmap(FIX_TEXT_POKE1, NULL);
}

size = sizeof(u32);
} else {
Expand All @@ -36,10 +95,16 @@ void __kprobes __patch_text(void *addr, unsigned int insn)
else
insn = __opcode_to_mem_arm(insn);

*(u32 *)addr = insn;
*(u32 *)waddr = insn;
size = sizeof(u32);
}

if (waddr != addr) {
flush_kernel_vmap_range(waddr, twopage ? size / 2 : size);
patch_unmap(FIX_TEXT_POKE0, &flags);
} else
__release(&patch_lock);

flush_icache_range((uintptr_t)(addr),
(uintptr_t)(addr) + size);
}
Expand All @@ -60,16 +125,5 @@ void __kprobes patch_text(void *addr, unsigned int insn)
.insn = insn,
};

if (cache_ops_need_broadcast()) {
stop_machine(patch_text_stop_machine, &patch, cpu_online_mask);
} else {
bool straddles_word = IS_ENABLED(CONFIG_THUMB2_KERNEL)
&& __opcode_is_thumb32(insn)
&& ((uintptr_t)addr & 2);

if (straddles_word)
stop_machine(patch_text_stop_machine, &patch, NULL);
else
__patch_text(addr, insn);
}
stop_machine(patch_text_stop_machine, &patch, NULL);
}
12 changes: 11 additions & 1 deletion arch/arm/kernel/patch.h
Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,16 @@
#define _ARM_KERNEL_PATCH_H

void patch_text(void *addr, unsigned int insn);
void __patch_text(void *addr, unsigned int insn);
void __patch_text_real(void *addr, unsigned int insn, bool remap);

static inline void __patch_text(void *addr, unsigned int insn)
{
__patch_text_real(addr, insn, true);
}

static inline void __patch_text_early(void *addr, unsigned int insn)
{
__patch_text_real(addr, insn, false);
}

#endif

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