From: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>
To: linuxppc-dev@lists.ozlabs.org, Russell Currey <ruscur@russell.cc>
Cc: ajd@linux.ibm.com, dja@axtens.net,
kernel-hardening@lists.openwall.com, npiggin@gmail.com
Subject: Re: [PATCH v8 2/7] powerpc/kprobes: Mark newly allocated probes as RO
Date: Thu, 02 Apr 2020 21:46:12 +0530 [thread overview]
Message-ID: <1585844035.o235bvxmq0.naveen@linux.ibm.com> (raw)
In-Reply-To: <20200402084053.188537-2-ruscur@russell.cc>
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@axtens.net>
> Signed-off-by: Russell Currey <ruscur@russell.cc>
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
> ---
> 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.
It seems to be handling the kretprobe itself properly, but seems to
crash on the return path. I haven't yet been able to work out what's
going wrong.
[ 0.517880] Kprobe smoke test: started
[ 0.626680] Oops: Exception in kernel mode, sig: 4 [#1]
[ 0.626708] LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA PowerNV
[ 0.626735] Modules linked in:
[ 0.626760] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.6.0-06592-g2e64694b9137 #51
[ 0.626795] NIP: c008000000020000 LR: c00000000021ce34 CTR: c00000000021c5f8
[ 0.626829] REGS: c0000000fd3e3860 TRAP: 0e40 Not tainted (5.6.0-06592-g2e64694b9137)
[ 0.626862] MSR: 9000000002089433 <SF,HV,VEC,EE,ME,SE,IR,DR,RI,LE> CR: 28000284 XER: 00040000
[ 0.626922] CFAR: c00000000000ef20 IRQMASK: 0
[ 0.626922] GPR00: c000000000052250 c0000000fd3e3af0 c000000002330200 000000002db8ad86
[ 0.626922] GPR04: 0000000000000000 c00000000006ba3c 0000000000000800 c0000000fd3a0000
[ 0.626922] GPR08: 0000000000000000 ffffffffaaaaaaab c0000000fd3a0000 0000000040000000
[ 0.626922] GPR12: c00000000021c5f0 c000000002520000 c000000000011790 0000000000000000
[ 0.626922] GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[ 0.626922] GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[ 0.626922] GPR24: c0000000020034bc c0000000012068b8 c000000002062e50 c0000000fd2319a0
[ 0.626922] GPR28: c000000000f5ebb0 0000000000000000 c0000000021bc278 c000000002458540
[ 0.627234] NIP [c008000000020000] 0xc008000000020000
[ 0.627264] LR [c00000000021ce34] init_test_probes+0x424/0x560
[ 0.627291] Call Trace:
[ 0.627313] [c0000000fd3e3af0] [c00000000021ce34] init_test_probes+0x424/0x560 (unreliable)
[ 0.627356] [c0000000fd3e3b90] [c00000000202de2c] init_kprobes+0x1a8/0x1c8
[ 0.627392] [c0000000fd3e3c00] [c000000000011140] do_one_initcall+0x60/0x2b0
[ 0.627432] [c0000000fd3e3cd0] [c000000002004674] kernel_init_freeable+0x2e0/0x3a0
[ 0.627471] [c0000000fd3e3db0] [c0000000000117ac] kernel_init+0x24/0x178
[ 0.627510] [c0000000fd3e3e20] [c00000000000c7a8] ret_from_kernel_thread+0x5c/0x74
[ 0.627543] Instruction dump:
[ 0.627562] XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX
[ 0.627607] XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX <00000000> 00000000 00000000 00000000
[ 0.627660] ---[ end trace 964ab92781f5d99d ]---
[ 0.629607]
- Naveen
next prev parent reply other threads:[~2020-04-02 16:20 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-02 8:40 [PATCH v8 1/7] powerpc/mm: Implement set_memory() routines Russell Currey
2020-04-02 8:40 ` [PATCH v8 2/7] powerpc/kprobes: Mark newly allocated probes as RO Russell Currey
2020-04-02 16:16 ` Naveen N. Rao [this message]
2020-04-02 18:48 ` Naveen N. Rao
2020-04-02 23:02 ` Russell Currey
2020-04-03 7:59 ` Russell Currey
2020-04-03 9:36 ` Naveen N. Rao
2020-04-03 9:42 ` Russell Currey
2020-04-03 10:03 ` Naveen N. Rao
2020-04-02 8:40 ` [PATCH v8 3/7] powerpc/mm/ptdump: debugfs handler for W+X checks at runtime Russell Currey
2020-04-02 8:40 ` [PATCH v8 4/7] powerpc: Set ARCH_HAS_STRICT_MODULE_RWX Russell Currey
2020-04-02 8:40 ` [PATCH v8 5/7] powerpc/configs: Enable STRICT_MODULE_RWX in skiroot_defconfig Russell Currey
2020-04-02 8:40 ` [PATCH v8 6/7] powerpc/mm: implement set_memory_attr() Russell Currey
2020-04-02 8:40 ` [PATCH v8 7/7] powerpc/32: use set_memory_attr() Russell Currey
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