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Message-ID: <a1745d9b-4bfc-50d2-8da6-7631ae2b24d0@meta.com>
Date: Wed, 30 Nov 2022 08:52:27 -0800
From: Yonghong Song <yhs@...a.com>
To: Chen Hu <hu1.chen@...el.com>
Cc: jpoimboe@...nel.org, memxor@...il.com, bpf@...r.kernel.org,
Pengfei Xu <pengfei.xu@...el.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
"H. Peter Anvin" <hpa@...or.com>,
Sean Christopherson <seanjc@...gle.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>,
Martin KaFai Lau <martin.lau@...ux.dev>,
Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>,
Stanislav Fomichev <sdf@...gle.com>,
Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Kees Cook <keescook@...omium.org>,
linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
netdev@...r.kernel.org
Subject: Re: [PATCH bpf v3] selftests/bpf: Fix "missing ENDBR" BUG for
destructor kfunc
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
> <TASK>
> 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)
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.
>
> 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 <hu1.chen@...el.com>
> Tested-by: Pengfei Xu <pengfei.xu@...el.com>
> ---
> 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);
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