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From: Russell Currey <ruscur@russell.cc>
To: linuxppc-dev@lists.ozlabs.org
Cc: Russell Currey <ruscur@russell.cc>,
	christophe.leroy@c-s.fr, joel@jms.id.au, mpe@ellerman.id.au,
	ajd@linux.ibm.com, dja@axtens.net, npiggin@gmail.com,
	kernel-hardening@lists.openwall.com
Subject: [PATCH v6 2/5] powerpc/kprobes: Mark newly allocated probes as RO
Date: Tue, 24 Dec 2019 16:55:42 +1100
Message-ID: <20191224055545.178462-3-ruscur@russell.cc> (raw)
In-Reply-To: <20191224055545.178462-1-ruscur@russell.cc>

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@axtens.net>
Signed-off-by: Russell Currey <ruscur@russell.cc>
---
 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));
 	}
 
+	set_memory_ro((unsigned long)p->ainsn.insn, 1);
+
 	p->ainsn.boostable = 0;
 	return ret;
 }
-- 
2.24.1


  parent reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-24  5:55 [PATCH v6 0/5] Implement STRICT_MODULE_RWX for powerpc Russell Currey
2019-12-24  5:55 ` [PATCH v6 1/5] powerpc/mm: Implement set_memory() routines Russell Currey
2020-01-08 12:52   ` Christophe Leroy
2020-02-03  0:46     ` Russell Currey
2020-02-03  7:06       ` Christophe Leroy
2020-01-20  8:35   ` Christophe Leroy
2019-12-24  5:55 ` Russell Currey [this message]
2020-01-08 16:48   ` [PATCH v6 2/5] powerpc/kprobes: Mark newly allocated probes as RO Christophe Leroy
2019-12-24  5:55 ` [PATCH v6 3/5] powerpc/mm/ptdump: debugfs handler for W+X checks at runtime Russell Currey
2019-12-31 17:14   ` Christophe Leroy
2020-01-07 10:48     ` Michael Ellerman
2019-12-24  5:55 ` [PATCH v6 4/5] powerpc: Set ARCH_HAS_STRICT_MODULE_RWX Russell Currey
2019-12-24  5:55 ` [PATCH v6 5/5] powerpc/configs: Enable STRICT_MODULE_RWX in skiroot_defconfig Russell Currey

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