Naveen N. Rao wrote:
Russell Currey wrote:
With CONFIG_STRICT_KERNEL_RWX=y and CONFIG_KPROBES=y, there will be one
W+X page at boot by default. This can be tested with
CONFIG_PPC_PTDUMP=y and CONFIG_PPC_DEBUG_WX=y set, and checking the
kernel log during boot.
powerpc doesn't implement its own alloc() for kprobes like other
architectures do, but we couldn't immediately mark RO anyway since we do
a memcpy to the page we allocate later. After that, nothing should be
allowed to modify the page, and write permissions are removed well
before the kprobe is armed.
The memcpy() would fail if >1 probes were allocated, so use
patch_instruction() instead which is safe for RO.
Reviewed-by: Daniel Axtens <dja@xxxxxxxxxx>
Signed-off-by: Russell Currey <ruscur@xxxxxxxxxx>
Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
---
arch/powerpc/kernel/kprobes.c | 17 +++++++++++++----
1 file changed, 13 insertions(+), 4 deletions(-)
diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index 81efb605113e..fa4502b4de35 100644
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -24,6 +24,8 @@
#include <asm/sstep.h>
#include <asm/sections.h>
#include <linux/uaccess.h>
+#include <linux/set_memory.h>
+#include <linux/vmalloc.h>
DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
@@ -102,6 +104,16 @@ kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset)
return addr;
}
+void *alloc_insn_page(void)
+{
+ void *page = vmalloc_exec(PAGE_SIZE);
+
+ if (page)
+ set_memory_ro((unsigned long)page, 1);
+
+ return page;
+}
+
This crashes for me with KPROBES_SANITY_TEST during the kretprobe test.
That isn't needed to reproduce this. After bootup, disabling optprobes
also shows the crash with kretprobes:
sysctl debug.kprobes-optimization=0
The problem happens to be with patch_instruction() in
arch_prepare_kprobe(). During boot, on kprobe init, we register a probe
on kretprobe_trampoline for use with kretprobes (see
arch_init_kprobes()). This results in an instruction slot being
allocated, and arch_prepare_kprobe() to be called for copying the
instruction (nop) at kretprobe_trampoline. patch_instruction() is
failing resulting in corrupt instruction which we try to emulate/single
step causing the crash.
- Naveen
