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Date: Mon, 15 Sep 2014 23:46:55 +0200 From: Daniel Borkmann <dborkman@...hat.com> To: Will Deacon <will.deacon@....com> CC: Catalin Marinas <Catalin.Marinas@....com>, "davem@...emloft.net" <davem@...emloft.net>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Zi Shen Lim <zlim.lnx@...il.com>, Alexei Starovoitov <ast@...mgrid.com> Subject: Re: [PATCH arm64-next v3] net: bpf: arm64: address randomize and write protect JIT code On 09/15/2014 11:30 PM, Will Deacon wrote: > Hi Daniel, > > One small comment than I forgot to mention before (see below). > > On Mon, Sep 15, 2014 at 09:20:23PM +0100, Daniel Borkmann wrote: >> This is the ARM64 variant for 314beb9bcab ("x86: bpf_jit_comp: secure bpf >> jit against spraying attacks"). >> >> Thanks to commit 11d91a770f1f ("arm64: Add CONFIG_DEBUG_SET_MODULE_RONX >> support") which added necessary infrastructure, we can now implement >> RO marking of eBPF generated JIT image pages and randomize start offset >> for the JIT code, so that it does not reside directly on a page boundary >> anymore. Likewise, the holes are filled with illegal instructions: here >> we use BRK #0x100 (opcode 0xd4202000) to trigger a fault in the kernel >> (unallocated BRKs would trigger a fault through do_debug_exception). This >> seems more reliable as we don't have a guaranteed undefined instruction >> space on ARM64. >> >> This is basically the ARM64 variant of what we already have in ARM via >> commit 55309dd3d4cd ("net: bpf: arm: address randomize and write protect >> JIT code"). Moreover, this commit also presents a merge resolution due to >> conflicts with commit 60a3b2253c41 ("net: bpf: make eBPF interpreter images >> read-only") as we don't use kfree() in bpf_jit_free() anymore to release >> the locked bpf_prog structure, but instead bpf_prog_unlock_free() through >> a different allocator. >> >> JIT tested on aarch64 with BPF test suite. >> >> Reference: http://mainisusuallyafunction.blogspot.com/2012/11/attacking-hardened-linux-systems-with.html >> Signed-off-by: Daniel Borkmann <dborkman@...hat.com> >> Cc: Zi Shen Lim <zlim.lnx@...il.com> >> Cc: Will Deacon <will.deacon@....com> >> Cc: Catalin Marinas <catalin.marinas@....com> >> Cc: David S. Miller <davem@...emloft.net> >> Cc: Alexei Starovoitov <ast@...mgrid.com> >> --- >> v2->v3: >> - Use cpu_to_le32() as suggested by Zi/Will >> v1->v2: >> - Use brk insn as suggested by Catalin >> Note: >> - This patch depends on net-next being merged to mainline due >> to the mentioned merge conflict. >> >> arch/arm64/net/bpf_jit_comp.c | 38 +++++++++++++++++++++++++++++--------- >> 1 file changed, 29 insertions(+), 9 deletions(-) >> >> diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c >> index 7ae3354..4b71779 100644 >> --- a/arch/arm64/net/bpf_jit_comp.c >> +++ b/arch/arm64/net/bpf_jit_comp.c >> @@ -19,7 +19,6 @@ >> #define pr_fmt(fmt) "bpf_jit: " fmt >> >> #include <linux/filter.h> >> -#include <linux/moduleloader.h> >> #include <linux/printk.h> >> #include <linux/skbuff.h> >> #include <linux/slab.h> >> @@ -119,6 +118,15 @@ static inline int bpf2a64_offset(int bpf_to, int bpf_from, >> return to - from; >> } >> >> +static void jit_fill_hole(void *area, unsigned int size) >> +{ >> + /* We use brk #0x100 to trigger a fault. */ >> + u32 *ptr; >> + /* We are guaranteed to have aligned memory. */ >> + for (ptr = area; size >= sizeof(u32); size -= sizeof(u32)) >> + *ptr++ = cpu_to_le32(0xd4202000); >> +} > > Please can you use the existing macros in debug-monitors.h for constructing > this value? We have AARCH64_BREAK_MON to get the BRK encoding, then you can > add an immediate to that file to reserve something for bpf. That way, we > make sure that other parts of the kernel don't accidentally repurpose your > fault code. Okay, no problem, I'll do that and respin tomorrow. Thanks, Daniel -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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