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Subject[PATCH] arm64: kprobe: make page to RO mode when allocate it
Date
Commit 1404d6f13e47 ("arm64: dump: Add checking for writable and exectuable pages")
has successfully identified code that leaves a page with W+X
permissions.

[ 3.245140] arm64/mm: Found insecure W+X mapping at address (____ptrval____)/0xffff000000d90000
[ 3.245771] WARNING: CPU: 0 PID: 1 at ../arch/arm64/mm/dump.c:232 note_page+0x410/0x420
[ 3.246141] Modules linked in:
[ 3.246653] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.19.0-rc5-next-20180928-00001-ge70ae259b853-dirty #62
[ 3.247008] Hardware name: linux,dummy-virt (DT)
[ 3.247347] pstate: 80000005 (Nzcv daif -PAN -UAO)
[ 3.247623] pc : note_page+0x410/0x420
[ 3.247898] lr : note_page+0x410/0x420
[ 3.248071] sp : ffff00000804bcd0
[ 3.248254] x29: ffff00000804bcd0 x28: ffff000009274000
[ 3.248578] x27: ffff00000921a000 x26: ffff80007dfff000
[ 3.248845] x25: ffff0000093f5000 x24: ffff000009526f6a
[ 3.249109] x23: 0000000000000004 x22: ffff000000d91000
[ 3.249396] x21: ffff000000d90000 x20: 0000000000000000
[ 3.249661] x19: ffff00000804bde8 x18: 0000000000000400
[ 3.249924] x17: 0000000000000000 x16: 0000000000000000
[ 3.250271] x15: ffffffffffffffff x14: 295f5f5f5f6c6176
[ 3.250594] x13: 7274705f5f5f5f28 x12: 2073736572646461
[ 3.250941] x11: 20746120676e6970 x10: 70616d20582b5720
[ 3.251252] x9 : 6572756365736e69 x8 : 3039643030303030
[ 3.251519] x7 : 306666666678302f x6 : ffff0000095467b2
[ 3.251802] x5 : 0000000000000000 x4 : 0000000000000000
[ 3.252060] x3 : 0000000000000000 x2 : ffffffffffffffff
[ 3.252323] x1 : 4d151327adc50b00 x0 : 0000000000000000
[ 3.252664] Call trace:
[ 3.252953] note_page+0x410/0x420
[ 3.253186] walk_pgd+0x12c/0x238
[ 3.253417] ptdump_check_wx+0x68/0xf8
[ 3.253637] mark_rodata_ro+0x68/0x98
[ 3.253847] kernel_init+0x38/0x160
[ 3.254103] ret_from_fork+0x10/0x18

Reworked to that when allocate a page it sets mode RO. Inspired by
commit 63fef14fc98a ("kprobes/x86: Make insn buffer always ROX and use text_poke()").

Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Laura Abbott <labbott@redhat.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Co-developed-by: Arnd Bergmann <arnd@arndb.de>
Co-developed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
---
arch/arm64/kernel/probes/kprobes.c | 27 ++++++++++++++++++++-------
1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
index 9b65132e789a..b842e908b423 100644
--- a/arch/arm64/kernel/probes/kprobes.c
+++ b/arch/arm64/kernel/probes/kprobes.c
@@ -23,7 +23,9 @@
#include <linux/slab.h>
#include <linux/stop_machine.h>
#include <linux/sched/debug.h>
+#include <linux/set_memory.h>
#include <linux/stringify.h>
+#include <linux/vmalloc.h>
#include <asm/traps.h>
#include <asm/ptrace.h>
#include <asm/cacheflush.h>
@@ -42,10 +44,21 @@ DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
static void __kprobes
post_kprobe_handler(struct kprobe_ctlblk *, struct pt_regs *);

+static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
+{
+ void *addrs[1];
+ u32 insns[1];
+
+ addrs[0] = (void *)addr;
+ insns[0] = (u32)opcode;
+
+ return aarch64_insn_patch_text(addrs, insns, 1);
+}
+
static void __kprobes arch_prepare_ss_slot(struct kprobe *p)
{
/* prepare insn slot */
- p->ainsn.api.insn[0] = cpu_to_le32(p->opcode);
+ patch_text(p->ainsn.api.insn, p->opcode);

flush_icache_range((uintptr_t) (p->ainsn.api.insn),
(uintptr_t) (p->ainsn.api.insn) +
@@ -118,15 +131,15 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
return 0;
}

-static int __kprobes patch_text(kprobe_opcode_t *addr, u32 opcode)
+void *alloc_insn_page(void)
{
- void *addrs[1];
- u32 insns[1];
+ void *page;

- addrs[0] = (void *)addr;
- insns[0] = (u32)opcode;
+ page = vmalloc_exec(PAGE_SIZE);
+ if (page)
+ set_memory_ro((unsigned long)page & PAGE_MASK, 1);

- return aarch64_insn_patch_text(addrs, insns, 1);
+ return page;
}

/* arm kprobe: install breakpoint in text */
--
2.19.1
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