[PATCH AUTOSEL for 4.4 008/101] kprobes/x86: Set kprobes pages read-only

[Sasha Levin]

From: Masami Hiramatsu <mhiramat@xxxxxxxxxx>

[ Upstream commit d0381c81c2f782fa2131178d11e0cfb23d50d631 ]

Set the pages which is used for kprobes' singlestep buffer
and optprobe's trampoline instruction buffer to readonly.
This can prevent unexpected (or unintended) instruction
modification.

This also passes rodata_test as below.

Without this patch, rodata_test shows a warning:

  WARNING: CPU: 0 PID: 1 at arch/x86/mm/dump_pagetables.c:235 note_page+0x7a9/0xa20
  x86/mm: Found insecure W+X mapping at address ffffffffa0000000/0xffffffffa0000000

With this fix, no W+X pages are found:

  x86/mm: Checked W+X mappings: passed, no W+X pages found.
  rodata_test: all tests were successful

Reported-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Ananth N Mavinakayanahalli <ananth@xxxxxxxxxxxxxxxxxx>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@xxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: David S . Miller <davem@xxxxxxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ye Xiaolong <xiaolong.ye@xxxxxxxxx>
Link: http://lkml.kernel.org/r/149076375592.22469.14174394514338612247.stgit@devbox
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
---
 arch/x86/kernel/kprobes/core.c | 4 ++++
 arch/x86/kernel/kprobes/opt.c  | 3 +++
 2 files changed, 7 insertions(+)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 5d11d01f75de..565e24e9ddf2 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -406,6 +406,8 @@ static int arch_copy_kprobe(struct kprobe *p)
 {
 	int ret;
 
+	set_memory_rw((unsigned long)p->ainsn.insn & PAGE_MASK, 1);
+
 	/* Copy an instruction with recovering if other optprobe modifies it.*/
 	ret = __copy_instruction(p->ainsn.insn, p->addr);
 	if (!ret)
@@ -420,6 +422,8 @@ static int arch_copy_kprobe(struct kprobe *p)
 	else
 		p->ainsn.boostable = -1;
 
+	set_memory_ro((unsigned long)p->ainsn.insn & PAGE_MASK, 1);
+
 	/* Check whether the instruction modifies Interrupt Flag or not */
 	p->ainsn.if_modifier = is_IF_modifier(p->ainsn.insn);
 
diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c
index ea8e2b846101..7aba9d6475a5 100644
--- a/arch/x86/kernel/kprobes/opt.c
+++ b/arch/x86/kernel/kprobes/opt.c
@@ -370,6 +370,7 @@ int arch_prepare_optimized_kprobe(struct optimized_kprobe *op,
 	}
 
 	buf = (u8 *)op->optinsn.insn;
+	set_memory_rw((unsigned long)buf & PAGE_MASK, 1);
 
 	/* Copy instructions into the out-of-line buffer */
 	ret = copy_optimized_instructions(buf + TMPL_END_IDX, op->kp.addr);
@@ -392,6 +393,8 @@ int arch_prepare_optimized_kprobe(struct optimized_kprobe *op,
 	synthesize_reljump(buf + TMPL_END_IDX + op->optinsn.size,
 			   (u8 *)op->kp.addr + op->optinsn.size);
 
+	set_memory_ro((unsigned long)buf & PAGE_MASK, 1);
+
 	flush_icache_range((unsigned long) buf,
 			   (unsigned long) buf + TMPL_END_IDX +
 			   op->optinsn.size + RELATIVEJUMP_SIZE);
-- 
2.14.1