Le 24/12/2019 à 06:55, Russell Currey a écrit :
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>
---
arch/powerpc/kernel/kprobes.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index 2d27ec4feee4..b72761f0c9e3 100644
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -24,6 +24,7 @@
#include <asm/sstep.h>
#include <asm/sections.h>
#include <linux/uaccess.h>
+#include <linux/set_memory.h>
DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
@@ -124,13 +125,14 @@ int arch_prepare_kprobe(struct kprobe *p)
}
if (!ret) {
- memcpy(p->ainsn.insn, p->addr,
- MAX_INSN_SIZE * sizeof(kprobe_opcode_t));
+ patch_instruction(p->ainsn.insn, *p->addr);
p->opcode = *p->addr;
flush_icache_range((unsigned long)p->ainsn.insn,
(unsigned long)p->ainsn.insn + sizeof(kprobe_opcode_t));
patch_instruction() already does the flush, no need to flush again with
flush_icache_range()
}
+ set_memory_ro((unsigned long)p->ainsn.insn, 1);
+
I don't really understand, why do you need to set this ro ? Or why do
you need to change the memcpy() to patch_instruction() if the area is
not already ro ?
If I understand correctly, p->ainsn.insn is within a special executable
page allocated via module_alloc(). Wouldn't it be more correct to modify
kprobe get_insn_slot() logic so that allocated page is ROX instead of RWX ?
p->ainsn.boostable = 0;
return ret;
}
Christophe
