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[2001:1ae9:1c2:4c00:726e:c10f:8833:ff22]) by smtp.gmail.com with ESMTPSA id q18-20020a1709066b1200b007bf988ce9f7sm1708749ejr.38.2022.12.01.03.50.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 Dec 2022 03:50:36 -0800 (PST) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Thu, 1 Dec 2022 12:50:34 +0100 To: "Chen, Hu1" Cc: Yonghong Song , jpoimboe@kernel.org, memxor@gmail.com, bpf@vger.kernel.org, Pengfei Xu , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Sean Christopherson , Paolo Bonzini , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Peter Zijlstra , Kees Cook , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, netdev@vger.kernel.org Subject: Re: [PATCH bpf v3] selftests/bpf: Fix "missing ENDBR" BUG for destructor kfunc Message-ID: References: <20221130101135.26806-1-hu1.chen@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Thu, Dec 01, 2022 at 04:07:56PM +0800, Chen, Hu1 wrote: > On 12/1/2022 12:52 AM, Yonghong Song wrote: > > > > > > On 11/30/22 2:11 AM, Chen Hu wrote: > > > With CONFIG_X86_KERNEL_IBT enabled, the test_verifier triggers the > > > following BUG: > > > > > >    traps: Missing ENDBR: bpf_kfunc_call_test_release+0x0/0x30 > > >    ------------[ cut here ]------------ > > >    kernel BUG at arch/x86/kernel/traps.c:254! > > >    invalid opcode: 0000 [#1] PREEMPT SMP > > >    > > >     asm_exc_control_protection+0x26/0x50 > > >    RIP: 0010:bpf_kfunc_call_test_release+0x0/0x30 > > >    Code: 00 48 c7 c7 18 f2 e1 b4 e8 0d ca 8c ff 48 c7 c0 00 f2 e1 b4 c3 > > >     0f 1f 44 00 00 66 0f 1f 00 0f 1f 44 00 00 0f 0b 31 c0 c3 66 90 > > >         <66> 0f 1f 00 0f 1f 44 00 00 48 85 ff 74 13 4c 8d 47 18 b8 ff ff ff > > >     bpf_map_free_kptrs+0x2e/0x70 > > >     array_map_free+0x57/0x140 > > >     process_one_work+0x194/0x3a0 > > >     worker_thread+0x54/0x3a0 > > >     ? rescuer_thread+0x390/0x390 > > >     kthread+0xe9/0x110 > > >     ? kthread_complete_and_exit+0x20/0x20 > > > > > > It turns out that ENDBR in bpf_kfunc_call_test_release() is converted to > > > NOP by apply_ibt_endbr(). > > > > > > The only text references to this function from kernel side are: > > > > > >    $ grep -r bpf_kfunc_call_test_release > > >    net/bpf/test_run.c:noinline void bpf_kfunc_call_test_release(...) > > >    net/bpf/test_run.c:BTF_ID_FLAGS(func, bpf_kfunc_call_test_release, ...) > > >    net/bpf/test_run.c:BTF_ID(func, bpf_kfunc_call_test_release) Alexei mentioned we could now move these ^^^ into kernel module: https://lore.kernel.org/bpf/CAADnVQJ4xaAacOUpzMG+bm2WK5u=1YLo5kLUL+RP3JZGW3Sfww@mail.gmail.com/ would it help? not sure objtool scans modules as well but we'd still need fix for bpf_obj_new_impl/bpf_obj_drop_impl below jirka > > > > We have some other function like this. For example, some newly added > > functions like bpf_obj_new_impl(), bpf_obj_drop_impl(), do they have > > the same missing endbr problem? If this is the case, we need a > > general solution. > > > > bpf_obj_new_impl(), bpf_obj_drop_impl() also miss the ENDBR. Below is > the disassembly on bpf-next kernel: > > (gdb) disas bpf_obj_drop_impl > Dump of assembler code for function bpf_obj_drop_impl: > 0xffffffff81288e40 <+0>: nopw (%rax) > 0xffffffff81288e44 <+4>: nopl 0x0(%rax,%rax,1) > 0xffffffff81288e49 <+9>: push %rbp > ... > > (gdb) disas bpf_obj_new_impl > Dump of assembler code for function bpf_obj_new_impl: > 0xffffffff81288cd0 <+0>: nopw (%rax) > 0xffffffff81288cd4 <+4>: nopl 0x0(%rax,%rax,1) > 0xffffffff81288cd9 <+9>: push %rbp > ... > > The first insn in the bpf_obj_new_impl has been converted from ENDBR to > nopw by objtool. If the function is indirectly called on IBT enabled CPU > (Tigerlake for example), #CP raise. > > Looks like the possible fix in this patch is general? > If we don't want to seal a funciton, we use macro IBT_NOSEAL to claim. > IBT_NOSEAL just creates throwaway dummy compile-time references to the > functions. The section is already thrown away when kernel run. See > commit e27e5bea956c by Josh Poimboeuf. > > > > > > > but it may be called from bpf program as kfunc. (no other caller from > > > kernel) > > > > > > This fix creates dummy references to destructor kfuncs so ENDBR stay > > > there. > > > > > > Also modify macro XXX_NOSEAL slightly: > > > - ASM_IBT_NOSEAL now stands for pure asm > > > - IBT_NOSEAL can be used directly in C > > > > > > Signed-off-by: Chen Hu > > > Tested-by: Pengfei Xu > > > --- > > > v3: > > > - Macro go to IBT related header as suggested by Jiri Olsa > > > - Describe reference to the func clearly in commit message as suggested > > >    by Peter Zijlstra and Jiri Olsa > > >   v2: https://lore.kernel.org/all/20221122073244.21279-1-hu1.chen@intel.com/ > > > > > > v1: https://lore.kernel.org/all/20221121085113.611504-1-hu1.chen@intel.com/ > > > > > >   arch/x86/include/asm/ibt.h | 6 +++++- > > >   arch/x86/kvm/emulate.c     | 2 +- > > >   net/bpf/test_run.c         | 5 +++++ > > >   3 files changed, 11 insertions(+), 2 deletions(-) > > > > > > diff --git a/arch/x86/include/asm/ibt.h b/arch/x86/include/asm/ibt.h > > > index 9b08082a5d9f..be86dc31661c 100644 > > > --- a/arch/x86/include/asm/ibt.h > > > +++ b/arch/x86/include/asm/ibt.h > > > @@ -36,11 +36,14 @@ > > >    * the function as needing to be "sealed" (i.e. ENDBR converted to NOP by > > >    * apply_ibt_endbr()). > > >    */ > > > -#define IBT_NOSEAL(fname)                \ > > > +#define ASM_IBT_NOSEAL(fname)                \ > > >       ".pushsection .discard.ibt_endbr_noseal\n\t"    \ > > >       _ASM_PTR fname "\n\t"                \ > > >       ".popsection\n\t" > > >   +#define IBT_NOSEAL(name)                \ > > > +    asm(ASM_IBT_NOSEAL(#name)) > > > + > > >   static inline __attribute_const__ u32 gen_endbr(void) > > >   { > > >       u32 endbr; > > > @@ -94,6 +97,7 @@ extern __noendbr void ibt_restore(u64 save); > > >   #ifndef __ASSEMBLY__ > > >     #define ASM_ENDBR > > > +#define ASM_IBT_NOSEAL(name) > > >   #define IBT_NOSEAL(name) > > >     #define __noendbr > > > diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c > > > index 4a43261d25a2..d870c8bb5831 100644 > > > --- a/arch/x86/kvm/emulate.c > > > +++ b/arch/x86/kvm/emulate.c > > > @@ -327,7 +327,7 @@ static int fastop(struct x86_emulate_ctxt *ctxt, fastop_t fop); > > >       ".type " name ", @function \n\t" \ > > >       name ":\n\t" \ > > >       ASM_ENDBR \ > > > -    IBT_NOSEAL(name) > > > +    ASM_IBT_NOSEAL(name) > > >     #define FOP_FUNC(name) \ > > >       __FOP_FUNC(#name) > > > diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c > > > index fcb3e6c5e03c..9e9c8e8d50d7 100644 > > > --- a/net/bpf/test_run.c > > > +++ b/net/bpf/test_run.c > > > @@ -601,6 +601,11 @@ noinline void bpf_kfunc_call_memb_release(struct prog_test_member *p) > > >   { > > >   } > > >   +#ifdef CONFIG_X86_KERNEL_IBT > > > +IBT_NOSEAL(bpf_kfunc_call_test_release); > > > +IBT_NOSEAL(bpf_kfunc_call_memb_release); > > > +#endif > > > + > > >   noinline void bpf_kfunc_call_memb1_release(struct prog_test_member1 *p) > > >   { > > >       WARN_ON_ONCE(1);