Commit ab0615e2 authored by Rabin Vincent's avatar Rabin Vincent Committed by Kees Cook
Browse files

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: default avatarRabin 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: default avatarKees Cook <keescook@chromium.org>
Acked-by: default avatarNicolas Pitre <nico@linaro.org>
parent 99b4ac9a

arch/arm/include/asm/fixmap.h

+4 −0
Original line number Diff line number Diff line
@@ -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

};

arch/arm/kernel/jump_label.c

+1 −1
Original line number Diff line number Diff line
@@ -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);

}

arch/arm/kernel/patch.c

+73 −19
Original line number Diff line number Diff line 
#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>
@@ -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 {
@@ -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);

}
@@ -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);

	}

}

arch/arm/kernel/patch.h

+11 −1
Original line number Diff line number Diff line
@@ -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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