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:
[ 10.041310] ------------[ cut here ]------------
[ 10.041717] WARNING: CPU: 0 PID: 1 at arch/x86/mm/dump_pagetables.c:235
note_page+0x7a9/0xa20
[ 10.042469] x86/mm: Found insecure W+X mapping at address
ffffffffa0000000/0xffffffffa0000000
[ 10.043073] Modules linked in:
[ 10.043317] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G B
4.11.0-rc1-00282-gc4bf2f7 #6
[ 10.043935] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.10.1-0-g8891697-prebuilt.qemu-project.org 04/01/2014
[ 10.044721] Call Trace:
[ 10.044898] dump_stack+0x63/0x8d
[ 10.045131] __warn+0x107/0x130
[ 10.045352] warn_slowpath_fmt+0x92/0xb0
[ 10.045623] ? __warn+0x130/0x130
[ 10.045856] ? 0xffffffffa0000000
[ 10.046104] ? 0xffffffffa0000000
[ 10.046337] note_page+0x7a9/0xa20
[ 10.046577] ptdump_walk_pgd_level_core+0x511/0x540
[ 10.046914] ? note_page+0xa20/0xa20
[ 10.047163] ? do_raw_spin_unlock+0x92/0x120
[ 10.047458] ? 0xffffffffa0000000
[ 10.047691] ? 0xffffffff81000000
[ 10.047924] ptdump_walk_pgd_level_checkwx+0x12/0x20
[ 10.048266] mark_rodata_ro+0x10e/0x120
[ 10.048533] ? rest_init+0xe0/0xe0
[ 10.048771] kernel_init+0x2a/0x120
[ 10.049016] ? rest_init+0xe0/0xe0
[ 10.049254] ret_from_fork+0x2c/0x40
[ 10.049503] ---[ end trace 1e4cda1ee3314caa ]---
[ 10.049861] x86/mm: Checked W+X mappings: FAILED, 2 W+X pages found.
[ 10.050349] rodata_test: all tests were successful
With this fix, no W+X pages found:
[ 10.130919] x86/mm: Checked W+X mappings: passed, no W+X pages found.
[ 10.131624] rodata_test: all tests were successful
Signed-off-by: Masami Hiramatsu <mhira...@kernel.org>
Reported-by: Andrey Ryabinin <aryabi...@virtuozzo.com>
---
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 3f084a0..0dc24e6 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -419,6 +419,8 @@ static int arch_copy_kprobe(struct kprobe *p)
{
int len;
+ set_memory_rw((unsigned long)p->ainsn.insn & PAGE_MASK, 1);
+
/* Copy an instruction with recovering if other optprobe modifies it.*/
len = __copy_instruction(p->ainsn.insn, p->addr);
if (!len)
@@ -430,6 +432,8 @@ static int arch_copy_kprobe(struct kprobe *p)
*/
prepare_boost(p, len);
+ 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 3e7c6e5..b121037 100644
--- a/arch/x86/kernel/kprobes/opt.c
+++ b/arch/x86/kernel/kprobes/opt.c
@@ -350,6 +350,7 @@ 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);
@@ -372,6 +373,8 @@ 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);
