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Date:   Fri, 18 Jun 2021 02:10:38 +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: <20210618021038.52c2f558@xhacker>
In-Reply-To: <20210618014648.1857a62a@xhacker>
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        <ae256a5d-70ac-3a5f-ca55-5e4210a0624c@ghiti.fr>
        <50ebc99c-f0a2-b4ea-fc9b-cd93a8324697@ghiti.fr>
        <20210618012731.345657bf@xhacker>
        <20210618014648.1857a62a@xhacker>
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On Fri, 18 Jun 2021 01:46:48 +0800
Jisheng Zhang <jszhang3@mail.ustc.edu.cn> wrote:

> On Fri, 18 Jun 2021 01:27:31 +0800
> Jisheng Zhang <jszhang3@mail.ustc.edu.cn> wrote:
>=20
> > 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.c=
n=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 ke=
rnel      =20
> > > >>>> panic     =20
> > > >>>> > with the config:     =20
> > > >>>> > > [=C2=A0=C2=A0=C2=A0 0.138553] Unable to handle kernel paging=
 request 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 No=
t 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_in=
it+0x1e/0x82
> > > >>>> > [=C2=A0=C2=A0=C2=A0 0.140609] epc : ffffffff8029806c ra : ffff=
ffff8033be78 sp :      =20
> > > >>>> ffffffe001647da0     =20
> > > >>>> > [=C2=A0=C2=A0=C2=A0 0.140878]=C2=A0 gp : ffffffff81134b08 tp :=
 ffffffe001654380 t0 :      =20
> > > >>>> ffffffff81201158     =20
> > > >>>> > [=C2=A0=C2=A0=C2=A0 0.141156]=C2=A0 t1 : 0000000000000002 t2 :=
 0000000000000154 s0 :      =20
> > > >>>> ffffffe001647dd0     =20
> > > >>>> > [=C2=A0=C2=A0=C2=A0 0.141424]=C2=A0 s1 : ffffffff80a43250 a0 :=
 ffffffff81201220 a1 :      =20
> > > >>>> 0000000000000000     =20
> > > >>>> > [=C2=A0=C2=A0=C2=A0 0.141654]=C2=A0 a2 : 000000000000003c a3 :=
 ffffffff81201258 a4 :      =20
> > > >>>> 0000000000000064     =20
> > > >>>> > [=C2=A0=C2=A0=C2=A0 0.141893]=C2=A0 a5 : ffffffff8029806c a6 :=
 0000000000000040 a7 :      =20
> > > >>>> ffffffffffffffff     =20
> > > >>>> > [=C2=A0=C2=A0=C2=A0 0.142126]=C2=A0 s2 : ffffffff81201220 s3 :=
 0000000000000009 s4 :      =20
> > > >>>> ffffffff81135088     =20
> > > >>>> > [=C2=A0=C2=A0=C2=A0 0.142353]=C2=A0 s5 : ffffffff81135038 s6 :=
 ffffffff8080ce80 s7 :      =20
> > > >>>> ffffffff80800438     =20
> > > >>>> > [=C2=A0=C2=A0=C2=A0 0.142584]=C2=A0 s8 : ffffffff80bc6578 s9 :=
 0000000000000008 s10:      =20
> > > >>>> ffffffff806000ac     =20
> > > >>>> > [=C2=A0=C2=A0=C2=A0 0.142810]=C2=A0 s11: 0000000000000000 t3 :=
 fffffffffffffffc t4 :      =20
> > > >>>> 0000000000000000     =20
> > > >>>> > [=C2=A0=C2=A0=C2=A0 0.143042]=C2=A0 t5 : 0000000000000155 t6 :=
 00000000000003ff
> > > >>>> > [=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+0x=
c4/0xfc
> > > >>>> > [=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_init=
call+0x3e/0x168
> > > >>>> > [=C2=A0=C2=A0=C2=A0 0.144278] [<ffffffff80600df0>] kernel_init=
_freeable+0x1c8/0x224
> > > >>>> > [=C2=A0=C2=A0=C2=A0 0.144479] [<ffffffff804868a8>] kernel_init=
+0x12/0x110
> > > >>>> > [=C2=A0=C2=A0=C2=A0 0.144658] [<ffffffff800022de>] ret_from_ex=
ception+0x0/0xc
> > > >>>> > [=C2=A0=C2=A0=C2=A0 0.145124] ---[ end trace f1e9643daa46d591 =
]---     =20
> > > >>>> > > After some investigation, I think I found the root cause: co=
mmit     =20
> > > >>>> > 2bfc6cd81bd ("move kernel mapping outside of linear mapping") =
moves
> > > >>>> > BPF JIT region after the kernel:     =20
> > > >>>> > > The &_end is unlikely aligned with PMD size, so the front bp=
f 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 o=
f      =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 =
_end=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 PM=
D size     =20
> > > >>>> > aligned. This patch acchieve this goal by restoring the BPF JI=
T      =20
> > > >>>> region     =20
> > > >>>> > to original position, I.E the 128MB before kernel .text sectio=
n.     =20
> > > >>>> But I disagree with your solution: I made sure modules and BPF=20
> > > >>>> programs get their own virtual regions to avoid worst case scena=
rio=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 regio=
n sit
> > > >>> between module and kernel.
> > > >>>
> > > >>> To address "make sure modules and BPF programs get their own virt=
ual=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_REG=
ION_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((unsigne=
d 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((unsigne=
d 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 (S=
Z_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((uns=
igned long)&_end)
> > > >>>> > -#define BPF_JIT_REGION_END=C2=A0=C2=A0=C2=A0 (BPF_JIT_REGION_=
START +      =20
> > > >>>> BPF_JIT_REGION_SIZE)     =20
> > > >>>> > +#define BPF_JIT_REGION_START=C2=A0=C2=A0=C2=A0 (BPF_JIT_REGIO=
N_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 (PA=
GE_OFFSET - BPF_JIT_REGION_SIZE)
> > > >>>> >=C2=A0=C2=A0 #define BPF_JIT_REGION_END=C2=A0=C2=A0=C2=A0 (VMAL=
LOC_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 modul=
es,=20
> > > > kernel and BPF:
> > > >=20
> > > >  =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 kasan_populate(kasan_me=
m_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 tha=
t=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 encompas=
ses=20
> > > BPF mapping */
> > >          kasan_populate(kasan_mem_to_shadow((const void *)MODULES_VAD=
DR),
> > > -                      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 cov=
er
> > kernel, bpf, and module:
> >=20
> >         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 =
+ SZ_2G));
> >  =20
>=20
> I made a mistake. Below patch works:
>=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)));

This isn't the key. I knew the reason now. kasan_init() has local vars named
as _start and _end, then MODULES_VADDR is defined as:
#define MODULES_VADDR   (PFN_ALIGN((unsigned long)&_end) - SZ_2G)

So MODULES_VADDR isn't what we expected. To fix it, we must rename the local
vars

>=20
> > 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_a=
ddr 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 =
was=20
> > > re-exposed in v6 of the patchset "Map the kernel with correct=20
> > > permissions the first time".
> > >    =20
> >=20
> >=20
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-riscv =20
>=20