Messages in this thread | | | Date | Thu, 17 Jun 2021 00:30:35 -0700 (PDT) | Subject | Re: [PATCH] riscv: Ensure BPF_JIT_REGION_START aligned with PMD size | From | Palmer Dabbelt <> |
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On Tue, 15 Jun 2021 17:03:28 PDT (-0700), jszhang3@mail.ustc.edu.cn wrote: > On Tue, 15 Jun 2021 20:54:19 +0200 > Alex Ghiti <alex@ghiti.fr> wrote: > >> Hi Jisheng, > > Hi Alex, > >> >> Le 14/06/2021 à 18:49, Jisheng Zhang a écrit : >> > From: Jisheng Zhang <jszhang@kernel.org> >> > >> > Andreas reported commit fc8504765ec5 ("riscv: bpf: Avoid breaking W^X") >> > breaks booting with one kind of config file, I reproduced a kernel panic >> > with the config: >> > >> > [ 0.138553] Unable to handle kernel paging request at virtual address ffffffff81201220 >> > [ 0.139159] Oops [#1] >> > [ 0.139303] Modules linked in: >> > [ 0.139601] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.13.0-rc5-default+ #1 >> > [ 0.139934] Hardware name: riscv-virtio,qemu (DT) >> > [ 0.140193] epc : __memset+0xc4/0xfc >> > [ 0.140416] ra : skb_flow_dissector_init+0x1e/0x82 >> > [ 0.140609] epc : ffffffff8029806c ra : ffffffff8033be78 sp : ffffffe001647da0 >> > [ 0.140878] gp : ffffffff81134b08 tp : ffffffe001654380 t0 : ffffffff81201158 >> > [ 0.141156] t1 : 0000000000000002 t2 : 0000000000000154 s0 : ffffffe001647dd0 >> > [ 0.141424] s1 : ffffffff80a43250 a0 : ffffffff81201220 a1 : 0000000000000000 >> > [ 0.141654] a2 : 000000000000003c a3 : ffffffff81201258 a4 : 0000000000000064 >> > [ 0.141893] a5 : ffffffff8029806c a6 : 0000000000000040 a7 : ffffffffffffffff >> > [ 0.142126] s2 : ffffffff81201220 s3 : 0000000000000009 s4 : ffffffff81135088 >> > [ 0.142353] s5 : ffffffff81135038 s6 : ffffffff8080ce80 s7 : ffffffff80800438 >> > [ 0.142584] s8 : ffffffff80bc6578 s9 : 0000000000000008 s10: ffffffff806000ac >> > [ 0.142810] s11: 0000000000000000 t3 : fffffffffffffffc t4 : 0000000000000000 >> > [ 0.143042] t5 : 0000000000000155 t6 : 00000000000003ff >> > [ 0.143220] status: 0000000000000120 badaddr: ffffffff81201220 cause: 000000000000000f >> > [ 0.143560] [<ffffffff8029806c>] __memset+0xc4/0xfc >> > [ 0.143859] [<ffffffff8061e984>] init_default_flow_dissectors+0x22/0x60 >> > [ 0.144092] [<ffffffff800010fc>] do_one_initcall+0x3e/0x168 >> > [ 0.144278] [<ffffffff80600df0>] kernel_init_freeable+0x1c8/0x224 >> > [ 0.144479] [<ffffffff804868a8>] kernel_init+0x12/0x110 >> > [ 0.144658] [<ffffffff800022de>] ret_from_exception+0x0/0xc >> > [ 0.145124] ---[ end trace f1e9643daa46d591 ]--- >> > >> > After some investigation, I think I found the root cause: commit >> > 2bfc6cd81bd ("move kernel mapping outside of linear mapping") moves >> > BPF JIT region after the kernel: >> > >> > The &_end is unlikely aligned with PMD size, so the front bpf jit >> > region sits with part of kernel .data section in one PMD size mapping. >> > 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 kernel >> > .data section RO too, so when we write to, for example memset the >> > .data section, MMU will trigger a store page fault. >> >> Good catch, we make sure no physical allocation happens between _end and >> the next PMD aligned address, but I missed this one. >> >> > >> > To fix the issue, we need to ensure the BPF JIT region is PMD size >> > aligned. This patch acchieve this goal by restoring the BPF JIT region >> > to original position, I.E the 128MB before kernel .text section. >> >> But I disagree with your solution: I made sure modules and BPF programs >> get their own virtual regions to avoid worst case scenario where one >> could allocate all the space and leave nothing to the other (we are >> limited to +- 2GB offset). Why don't just align BPF_JIT_REGION_START to >> the next PMD aligned address? > > Originally, I planed to fix the issue by aligning BPF_JIT_REGION_START, but > IIRC, BPF experts are adding (or have added) "Calling kernel functions from BPF" > feature, there's a risk that BPF JIT region is beyond the 2GB of 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 virtual regions", > what about something as below (applied against this patch)? > > diff --git a/arch/riscv/include/asm/pgtable.h 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 @@ > #define BPF_JIT_REGION_SIZE (SZ_128M) > #ifdef CONFIG_64BIT > #define BPF_JIT_REGION_START (BPF_JIT_REGION_END - BPF_JIT_REGION_SIZE) > -#define BPF_JIT_REGION_END (MODULES_END) > +#define BPF_JIT_REGION_END (PFN_ALIGN((unsigned long)&_start)) > #else > #define BPF_JIT_REGION_START (PAGE_OFFSET - BPF_JIT_REGION_SIZE) > #define BPF_JIT_REGION_END (VMALLOC_END) > @@ -40,7 +40,7 @@ > /* Modules always live before the kernel */ > #ifdef CONFIG_64BIT > #define MODULES_VADDR (PFN_ALIGN((unsigned long)&_end) - SZ_2G) > -#define MODULES_END (PFN_ALIGN((unsigned long)&_start)) > +#define MODULES_END (BPF_JIT_REGION_END) > #endif > > > >> >> Again, good catch, thanks, >> >> Alex >> >> > >> > Reported-by: Andreas Schwab <schwab@linux-m68k.org> >> > Signed-off-by: Jisheng Zhang <jszhang@kernel.org> >> > --- >> > arch/riscv/include/asm/pgtable.h | 5 ++--- >> > 1 file changed, 2 insertions(+), 3 deletions(-) >> > >> > diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h >> > index 9469f464e71a..380cd3a7e548 100644 >> > --- a/arch/riscv/include/asm/pgtable.h >> > +++ b/arch/riscv/include/asm/pgtable.h >> > @@ -30,9 +30,8 @@ >> > >> > #define BPF_JIT_REGION_SIZE (SZ_128M) >> > #ifdef CONFIG_64BIT >> > -/* KASLR should leave at least 128MB for BPF after the kernel */ >> > -#define BPF_JIT_REGION_START PFN_ALIGN((unsigned long)&_end) >> > -#define BPF_JIT_REGION_END (BPF_JIT_REGION_START + BPF_JIT_REGION_SIZE) >> > +#define BPF_JIT_REGION_START (BPF_JIT_REGION_END - BPF_JIT_REGION_SIZE) >> > +#define BPF_JIT_REGION_END (MODULES_END) >> > #else >> > #define BPF_JIT_REGION_START (PAGE_OFFSET - BPF_JIT_REGION_SIZE) >> > #define BPF_JIT_REGION_END (VMALLOC_END) >> >
This, when applied onto fixes, is breaking early boot on KASAN configurations for me.
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