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Date:   Fri, 18 Jun 2021 01:46:48 +0800
From:   Jisheng Zhang <jszhang3@mail.ustc.edu.cn>
To:     Alex Ghiti <alex@ghiti.fr>
Cc:     Palmer Dabbelt <palmer@dabbelt.com>, schwab@linux-m68k.org,
        Paul Walmsley <paul.walmsley@sifive.com>,
        aou@eecs.berkeley.edu, ryabinin.a.a@gmail.com, glider@google.com,
        andreyknvl@gmail.com, dvyukov@google.com, bjorn@kernel.org,
        ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org,
        kafai@fb.com, songliubraving@fb.com, yhs@fb.com,
        john.fastabend@gmail.com, kpsingh@kernel.org,
        luke.r.nels@gmail.com, xi.wang@gmail.com,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
        kasan-dev@googlegroups.com, netdev@vger.kernel.org,
        bpf@vger.kernel.org
Subject: Re: [PATCH] riscv: Ensure BPF_JIT_REGION_START aligned with PMD
 size
Message-ID: <20210618014648.1857a62a@xhacker>
In-Reply-To: <20210618012731.345657bf@xhacker>
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        <ae256a5d-70ac-3a5f-ca55-5e4210a0624c@ghiti.fr>
        <50ebc99c-f0a2-b4ea-fc9b-cd93a8324697@ghiti.fr>
        <20210618012731.345657bf@xhacker>
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On Fri, 18 Jun 2021 01:27:31 +0800
Jisheng Zhang <jszhang3@mail.ustc.edu.cn> wrote:

> On Thu, 17 Jun 2021 16:18:54 +0200
> Alex Ghiti <alex@ghiti.fr> wrote:
>=20
> > Le 17/06/2021 =C3=A0 10:09, Alex Ghiti a =C3=A9crit=C2=A0: =20
> > > Le 17/06/2021 =C3=A0 09:30, Palmer Dabbelt a =C3=A9crit=C2=A0:   =20
> > >> On Tue, 15 Jun 2021 17:03:28 PDT (-0700), jszhang3@mail.ustc.edu.cn=
=20
> > >> wrote:   =20
> > >>> On Tue, 15 Jun 2021 20:54:19 +0200
> > >>> Alex Ghiti <alex@ghiti.fr> wrote:
> > >>>   =20
> > >>>> Hi Jisheng,   =20
> > >>>
> > >>> Hi Alex,
> > >>>   =20
> > >>>>
> > >>>> Le 14/06/2021 =C3=A0 18:49, Jisheng Zhang a =C3=A9crit=C2=A0:   =20
> > >>>> > From: Jisheng Zhang <jszhang@kernel.org>   =20
> > >>>> > > Andreas reported commit fc8504765ec5 ("riscv: bpf: Avoid    =20
> > >>>> breaking W^X")   =20
> > >>>> > breaks booting with one kind of config file, I reproduced a kern=
el    =20
> > >>>> panic   =20
> > >>>> > with the config:   =20
> > >>>> > > [=C2=A0=C2=A0=C2=A0 0.138553] Unable to handle kernel paging r=
equest at virtual    =20
> > >>>> address ffffffff81201220   =20
> > >>>> > [=C2=A0=C2=A0=C2=A0 0.139159] Oops [#1]
> > >>>> > [=C2=A0=C2=A0=C2=A0 0.139303] Modules linked in:
> > >>>> > [=C2=A0=C2=A0=C2=A0 0.139601] CPU: 0 PID: 1 Comm: swapper/0 Not =
tainted    =20
> > >>>> 5.13.0-rc5-default+ #1   =20
> > >>>> > [=C2=A0=C2=A0=C2=A0 0.139934] Hardware name: riscv-virtio,qemu (=
DT)
> > >>>> > [=C2=A0=C2=A0=C2=A0 0.140193] epc : __memset+0xc4/0xfc
> > >>>> > [=C2=A0=C2=A0=C2=A0 0.140416]=C2=A0 ra : skb_flow_dissector_init=
+0x1e/0x82
> > >>>> > [=C2=A0=C2=A0=C2=A0 0.140609] epc : ffffffff8029806c ra : ffffff=
ff8033be78 sp :    =20
> > >>>> ffffffe001647da0   =20
> > >>>> > [=C2=A0=C2=A0=C2=A0 0.140878]=C2=A0 gp : ffffffff81134b08 tp : f=
fffffe001654380 t0 :    =20
> > >>>> ffffffff81201158   =20
> > >>>> > [=C2=A0=C2=A0=C2=A0 0.141156]=C2=A0 t1 : 0000000000000002 t2 : 0=
000000000000154 s0 :    =20
> > >>>> ffffffe001647dd0   =20
> > >>>> > [=C2=A0=C2=A0=C2=A0 0.141424]=C2=A0 s1 : ffffffff80a43250 a0 : f=
fffffff81201220 a1 :    =20
> > >>>> 0000000000000000   =20
> > >>>> > [=C2=A0=C2=A0=C2=A0 0.141654]=C2=A0 a2 : 000000000000003c a3 : f=
fffffff81201258 a4 :    =20
> > >>>> 0000000000000064   =20
> > >>>> > [=C2=A0=C2=A0=C2=A0 0.141893]=C2=A0 a5 : ffffffff8029806c a6 : 0=
000000000000040 a7 :    =20
> > >>>> ffffffffffffffff   =20
> > >>>> > [=C2=A0=C2=A0=C2=A0 0.142126]=C2=A0 s2 : ffffffff81201220 s3 : 0=
000000000000009 s4 :    =20
> > >>>> ffffffff81135088   =20
> > >>>> > [=C2=A0=C2=A0=C2=A0 0.142353]=C2=A0 s5 : ffffffff81135038 s6 : f=
fffffff8080ce80 s7 :    =20
> > >>>> ffffffff80800438   =20
> > >>>> > [=C2=A0=C2=A0=C2=A0 0.142584]=C2=A0 s8 : ffffffff80bc6578 s9 : 0=
000000000000008 s10:    =20
> > >>>> ffffffff806000ac   =20
> > >>>> > [=C2=A0=C2=A0=C2=A0 0.142810]=C2=A0 s11: 0000000000000000 t3 : f=
ffffffffffffffc t4 :    =20
> > >>>> 0000000000000000   =20
> > >>>> > [=C2=A0=C2=A0=C2=A0 0.143042]=C2=A0 t5 : 0000000000000155 t6 : 0=
0000000000003ff
> > >>>> > [=C2=A0=C2=A0=C2=A0 0.143220] status: 0000000000000120 badaddr: =
ffffffff81201220    =20
> > >>>> cause: 000000000000000f   =20
> > >>>> > [=C2=A0=C2=A0=C2=A0 0.143560] [<ffffffff8029806c>] __memset+0xc4=
/0xfc
> > >>>> > [=C2=A0=C2=A0=C2=A0 0.143859] [<ffffffff8061e984>]    =20
> > >>>> init_default_flow_dissectors+0x22/0x60   =20
> > >>>> > [=C2=A0=C2=A0=C2=A0 0.144092] [<ffffffff800010fc>] do_one_initca=
ll+0x3e/0x168
> > >>>> > [=C2=A0=C2=A0=C2=A0 0.144278] [<ffffffff80600df0>] kernel_init_f=
reeable+0x1c8/0x224
> > >>>> > [=C2=A0=C2=A0=C2=A0 0.144479] [<ffffffff804868a8>] kernel_init+0=
x12/0x110
> > >>>> > [=C2=A0=C2=A0=C2=A0 0.144658] [<ffffffff800022de>] ret_from_exce=
ption+0x0/0xc
> > >>>> > [=C2=A0=C2=A0=C2=A0 0.145124] ---[ end trace f1e9643daa46d591 ]-=
--   =20
> > >>>> > > After some investigation, I think I found the root cause: comm=
it   =20
> > >>>> > 2bfc6cd81bd ("move kernel mapping outside of linear mapping") mo=
ves
> > >>>> > BPF JIT region after the kernel:   =20
> > >>>> > > The &_end is unlikely aligned with PMD size, so the front bpf =
jit   =20
> > >>>> > region sits with part of kernel .data section in one PMD size   =
 =20
> > >>>> mapping.   =20
> > >>>> > But kernel is mapped in PMD SIZE, when bpf_jit_binary_lock_ro() =
is
> > >>>> > called to make the first bpf jit prog ROX, we will make part of =
   =20
> > >>>> kernel   =20
> > >>>> > .data section RO too, so when we write to, for example memset the
> > >>>> > .data section, MMU will trigger a store page fault.   =20
> > >>>> Good catch, we make sure no physical allocation happens between _e=
nd=20
> > >>>> and the next PMD aligned address, but I missed this one.
> > >>>>   =20
> > >>>> > > To fix the issue, we need to ensure the BPF JIT region is PMD =
size   =20
> > >>>> > aligned. This patch acchieve this goal by restoring the BPF JIT =
   =20
> > >>>> region   =20
> > >>>> > to original position, I.E the 128MB before kernel .text section.=
   =20
> > >>>> But I disagree with your solution: I made sure modules and BPF=20
> > >>>> programs get their own virtual regions to avoid worst case scenari=
o=20
> > >>>> where one could allocate all the space and leave nothing to the=20
> > >>>> other (we are limited to +- 2GB offset). Why don't just align=20
> > >>>> BPF_JIT_REGION_START to the next PMD aligned address?   =20
> > >>>
> > >>> Originally, I planed to fix the issue by aligning=20
> > >>> BPF_JIT_REGION_START, but
> > >>> IIRC, BPF experts are adding (or have added) "Calling kernel=20
> > >>> functions from BPF"
> > >>> feature, there's a risk that BPF JIT region is beyond the 2GB of=20
> > >>> module region:
> > >>>
> > >>> ------
> > >>> module
> > >>> ------
> > >>> kernel
> > >>> ------
> > >>> BPF_JIT
> > >>>
> > >>> So I made this patch finally. In this patch, we let BPF JIT region =
sit
> > >>> between module and kernel.
> > >>>
> > >>> To address "make sure modules and BPF programs get their own virtua=
l=20
> > >>> regions",
> > >>> what about something as below (applied against this patch)?
> > >>>
> > >>> diff --git a/arch/riscv/include/asm/pgtable.h=20
> > >>> b/arch/riscv/include/asm/pgtable.h
> > >>> index 380cd3a7e548..da1158f10b09 100644
> > >>> --- a/arch/riscv/include/asm/pgtable.h
> > >>> +++ b/arch/riscv/include/asm/pgtable.h
> > >>> @@ -31,7 +31,7 @@
> > >>> =C2=A0#define BPF_JIT_REGION_SIZE=C2=A0=C2=A0=C2=A0 (SZ_128M)
> > >>> =C2=A0#ifdef CONFIG_64BIT
> > >>> =C2=A0#define BPF_JIT_REGION_START=C2=A0=C2=A0=C2=A0 (BPF_JIT_REGIO=
N_END -=20
> > >>> BPF_JIT_REGION_SIZE)
> > >>> -#define BPF_JIT_REGION_END=C2=A0=C2=A0=C2=A0 (MODULES_END)
> > >>> +#define BPF_JIT_REGION_END=C2=A0=C2=A0=C2=A0 (PFN_ALIGN((unsigned =
long)&_start))
> > >>> =C2=A0#else
> > >>> =C2=A0#define BPF_JIT_REGION_START=C2=A0=C2=A0=C2=A0 (PAGE_OFFSET -=
 BPF_JIT_REGION_SIZE)
> > >>> =C2=A0#define BPF_JIT_REGION_END=C2=A0=C2=A0=C2=A0 (VMALLOC_END)
> > >>> @@ -40,7 +40,7 @@
> > >>> =C2=A0/* Modules always live before the kernel */
> > >>> =C2=A0#ifdef CONFIG_64BIT
> > >>> =C2=A0#define MODULES_VADDR=C2=A0=C2=A0=C2=A0 (PFN_ALIGN((unsigned =
long)&_end) - SZ_2G)
> > >>> -#define MODULES_END=C2=A0=C2=A0=C2=A0 (PFN_ALIGN((unsigned long)&_=
start))
> > >>> +#define MODULES_END=C2=A0=C2=A0=C2=A0 (BPF_JIT_REGION_END)
> > >>> =C2=A0#endif
> > >>>
> > >>>
> > >>>   =20
> > >>>>
> > >>>> Again, good catch, thanks,
> > >>>>
> > >>>> Alex
> > >>>>   =20
> > >>>> > > Reported-by: Andreas Schwab <schwab@linux-m68k.org>   =20
> > >>>> > Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> > >>>> > ---
> > >>>> >=C2=A0=C2=A0 arch/riscv/include/asm/pgtable.h | 5 ++---
> > >>>> >=C2=A0=C2=A0 1 file changed, 2 insertions(+), 3 deletions(-)   =20
> > >>>> > > diff --git a/arch/riscv/include/asm/pgtable.h    =20
> > >>>> b/arch/riscv/include/asm/pgtable.h   =20
> > >>>> > index 9469f464e71a..380cd3a7e548 100644
> > >>>> > --- a/arch/riscv/include/asm/pgtable.h
> > >>>> > +++ b/arch/riscv/include/asm/pgtable.h
> > >>>> > @@ -30,9 +30,8 @@   =20
> > >>>> > >=C2=A0=C2=A0 #define BPF_JIT_REGION_SIZE=C2=A0=C2=A0=C2=A0 (SZ_=
128M)   =20
> > >>>> >=C2=A0=C2=A0 #ifdef CONFIG_64BIT
> > >>>> > -/* KASLR should leave at least 128MB for BPF after the kernel */
> > >>>> > -#define BPF_JIT_REGION_START=C2=A0=C2=A0=C2=A0 PFN_ALIGN((unsig=
ned long)&_end)
> > >>>> > -#define BPF_JIT_REGION_END=C2=A0=C2=A0=C2=A0 (BPF_JIT_REGION_ST=
ART +    =20
> > >>>> BPF_JIT_REGION_SIZE)   =20
> > >>>> > +#define BPF_JIT_REGION_START=C2=A0=C2=A0=C2=A0 (BPF_JIT_REGION_=
END -    =20
> > >>>> BPF_JIT_REGION_SIZE)   =20
> > >>>> > +#define BPF_JIT_REGION_END=C2=A0=C2=A0=C2=A0 (MODULES_END)
> > >>>> >=C2=A0=C2=A0 #else
> > >>>> >=C2=A0=C2=A0 #define BPF_JIT_REGION_START=C2=A0=C2=A0=C2=A0 (PAGE=
_OFFSET - BPF_JIT_REGION_SIZE)
> > >>>> >=C2=A0=C2=A0 #define BPF_JIT_REGION_END=C2=A0=C2=A0=C2=A0 (VMALLO=
C_END)
> > >>>> >    =20
> > >>
> > >> This, when applied onto fixes, is breaking early boot on KASAN=20
> > >> configurations for me.   =20
>=20
> I can reproduce this issue.
>=20
> > >=20
> > > Not surprising, I took a shortcut when initializing KASAN for modules=
,=20
> > > kernel and BPF:
> > >=20
> > >  =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 kasan_populate(kasan_mem_=
to_shadow((const void *)MODULES_VADDR),
> > >  =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 kasan_me=
m_to_shadow((const void=20
> > > *)BPF_JIT_REGION_END));
> > >=20
> > > The kernel is then not covered, I'm taking a look at how to fix that=
=20
> > > properly.
> > >   =20
> >=20
> > The following based on "riscv: Introduce structure that group all=20
> > variables regarding kernel mapping" fixes the issue:
> >=20
> > diff --git a/arch/riscv/mm/kasan_init.c b/arch/riscv/mm/kasan_init.c
> > index 9daacae93e33..2a45ea909e7f 100644
> > --- a/arch/riscv/mm/kasan_init.c
> > +++ b/arch/riscv/mm/kasan_init.c
> > @@ -199,9 +199,12 @@ void __init kasan_init(void)
> >                  kasan_populate(kasan_mem_to_shadow(start),=20
> > kasan_mem_to_shadow(end));
> >          }
> >=20
> > -       /* Populate kernel, BPF, modules mapping */
> > +       /* Populate BPF and modules mapping: modules mapping encompasse=
s=20
> > BPF mapping */
> >          kasan_populate(kasan_mem_to_shadow((const void *)MODULES_VADDR=
),
> > -                      kasan_mem_to_shadow((const void=20
> > *)BPF_JIT_REGION_END));
> > +                      kasan_mem_to_shadow((const void *)MODULES_END));
> > +       /* Populate kernel mapping */
> > +       kasan_populate(kasan_mem_to_shadow((const void=20
> > *)kernel_map.virt_addr),
> > +                      kasan_mem_to_shadow((const void=20
> > *)kernel_map.virt_addr + kernel_map.size));
> > =20
> If this patch works, maybe we can still use one kasan_populate() to cover
> kernel, bpf, and module:
>=20
>         kasan_populate(kasan_mem_to_shadow((const void *)MODULES_VADDR),
> -                      kasan_mem_to_shadow((const void *)BPF_JIT_REGION_E=
ND));
> +                      kasan_mem_to_shadow((const void *)MODULES_VADDR + =
SZ_2G));
>=20

I made a mistake. Below patch works:

        kasan_populate(kasan_mem_to_shadow((const void *)MODULES_VADDR),
-                      kasan_mem_to_shadow((const void *)BPF_JIT_REGION_END=
));
+                      kasan_mem_to_shadow((const void *)(MODULES_VADDR + S=
Z_2G)));

> However, both can't solve the early boot hang issue. I'm not sure what's =
missing.
>=20
> I applied your patch on rc6 + solution below "replace kernel_map.virt_add=
r with kernel_virt_addr and
> kernel_map.size with load_sz"
>=20
>=20
> Thanks
> =20
> >=20
> > Without the mentioned patch, replace kernel_map.virt_addr with=20
> > kernel_virt_addr and kernel_map.size with load_sz. Note that load_sz wa=
s=20
> > re-exposed in v6 of the patchset "Map the kernel with correct=20
> > permissions the first time".
> >  =20
>=20
>=20
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