From mboxrd@z Thu Jan 1 00:00:00 1970 From: Will Deacon Subject: Re: [PATCH v4 2/2] arm64/bpf: don't allocate BPF JIT programs in module memory Date: Fri, 30 Nov 2018 18:26:29 +0000 Message-ID: <20181130182629.GA16085@arm.com> References: <20181123221804.440-1-ard.biesheuvel@linaro.org> <20181123221804.440-3-ard.biesheuvel@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-kernel@vger.kernel.org, Daniel Borkmann , Alexei Starovoitov , Rick Edgecombe , Eric Dumazet , Jann Horn , Kees Cook , Jessica Yu , Arnd Bergmann , Catalin Marinas , Mark Rutland , "David S. Miller" , linux-arm-kernel@lists.infradead.org, netdev@vger.kernel.org To: Ard Biesheuvel Return-path: Content-Disposition: inline In-Reply-To: <20181123221804.440-3-ard.biesheuvel@linaro.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Fri, Nov 23, 2018 at 11:18:04PM +0100, Ard Biesheuvel wrote: > The arm64 module region is a 128 MB region that is kept close to > the core kernel, in order to ensure that relative branches are > always in range. So using the same region for programs that do > not have this restriction is wasteful, and preferably avoided. > > Now that the core BPF JIT code permits the alloc/free routines to > be overridden, implement them by vmalloc()/vfree() calls from a > dedicated 128 MB region set aside for BPF programs. This ensures > that BPF programs are still in branching range of each other, which > is something the JIT currently depends upon (and is not guaranteed > when using module_alloc() on KASLR kernels like we do currently). > It also ensures that placement of BPF programs does not correlate > with the placement of the core kernel or modules, making it less > likely that leaking the former will reveal the latter. > > This also solves an issue under KASAN, where shadow memory is > needlessly allocated for all BPF programs (which don't require KASAN > shadow pages since they are not KASAN instrumented) > > Signed-off-by: Ard Biesheuvel > --- > arch/arm64/include/asm/memory.h | 5 ++++- > arch/arm64/net/bpf_jit_comp.c | 13 +++++++++++++ > 2 files changed, 17 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h > index b96442960aea..ee20fc63899c 100644 > --- a/arch/arm64/include/asm/memory.h > +++ b/arch/arm64/include/asm/memory.h > @@ -62,8 +62,11 @@ > #define PAGE_OFFSET (UL(0xffffffffffffffff) - \ > (UL(1) << (VA_BITS - 1)) + 1) > #define KIMAGE_VADDR (MODULES_END) > +#define BPF_JIT_REGION_START (VA_START + KASAN_SHADOW_SIZE) > +#define BPF_JIT_REGION_SIZE (SZ_128M) > +#define BPF_JIT_REGION_END (BPF_JIT_REGION_START + BPF_JIT_REGION_SIZE) > #define MODULES_END (MODULES_VADDR + MODULES_VSIZE) > -#define MODULES_VADDR (VA_START + KASAN_SHADOW_SIZE) > +#define MODULES_VADDR (BPF_JIT_REGION_END) > #define MODULES_VSIZE (SZ_128M) > #define VMEMMAP_START (PAGE_OFFSET - VMEMMAP_SIZE) > #define PCI_IO_END (VMEMMAP_START - SZ_2M) > diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c > index a6fdaea07c63..76c2ab40c02d 100644 > --- a/arch/arm64/net/bpf_jit_comp.c > +++ b/arch/arm64/net/bpf_jit_comp.c > @@ -940,3 +940,16 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *prog) > tmp : orig_prog); > return prog; > } > + > +void *bpf_jit_alloc_exec(unsigned long size) > +{ > + return __vmalloc_node_range(size, PAGE_SIZE, BPF_JIT_REGION_START, > + BPF_JIT_REGION_END, GFP_KERNEL, > + PAGE_KERNEL_EXEC, 0, NUMA_NO_NODE, > + __builtin_return_address(0)); I guess we'll want VM_IMMEDIATE_UNMAP here if Rich gets that merged. In the meantime, I wonder if it's worth zeroing the region in bpf_jit_free_exec()? (although we'd need the size information...). Will