Re: [PATCH 4/5] RISC-V: Protect .init.text & .init.data

From: Greentime Hu <greentime.hu@sifive.com>
To: Atish Patra <atishp@atishpatra.org>
Cc: Atish Patra <atish.patra@wdc.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Kees Cook <keescook@chromium.org>,
	Anup Patel <anup@brainfault.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-riscv <linux-riscv@lists.infradead.org>,
	Guo Ren <guoren@linux.alibaba.com>,
	Palmer Dabbelt <palmer@dabbelt.com>, Zong Li <zong.li@sifive.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Borislav Petkov <bp@suse.de>,
	Michel Lespinasse <walken@google.com>,
	Ard Biesheuvel <ardb@kernel.org>
Subject: Re: [PATCH 4/5] RISC-V: Protect .init.text & .init.data
Date: Tue, 13 Oct 2020 11:08:00 +0800	[thread overview]
Message-ID: <CAHCEehJJmLQ6W5AdH+hEZSJxpDC8HG0UN=EGt9M0Tp5NTfQnaw@mail.gmail.com> (raw)
In-Reply-To: <CAOnJCULZMRu+sHmnjoBwtvaB3BjmCiZLzYxNOeWZmoYLKG+wTw@mail.gmail.com>

Atish Patra <atishp@atishpatra.org> 於 2020年10月13日 週二 上午9:28寫道：
>
> On Mon, Oct 12, 2020 at 4:26 PM Atish Patra <atishp@atishpatra.org> wrote:
> >
> > On Mon, Oct 12, 2020 at 6:15 AM Greentime Hu <greentime.hu@sifive.com> wrote:
> > >
> > > Atish Patra <atish.patra@wdc.com> 於 2020年10月10日 週六 上午5:13寫道：
> > > >
> > > > Currently, .init.text & .init.data are intermixed which makes it impossible
> > > > apply different permissions to them. .init.data shouldn't need exec
> > > > permissions while .init.text shouldn't have write permission.
> > > >
> > > > Keep them in separate sections so that different permissions are applied to
> > > > each section. This improves the kernel protection under
> > > > CONFIG_STRICT_KERNEL_RWX. We also need to restore the permissions for the
> > > > entire _init section after it is freed so that those pages can be used for
> > > > other purpose.
> > > >
> > > > Signed-off-by: Atish Patra <atish.patra@wdc.com>
> > > > ---
> > > >  arch/riscv/include/asm/sections.h   |  2 ++
> > > >  arch/riscv/include/asm/set_memory.h |  2 ++
> > > >  arch/riscv/kernel/setup.c           |  4 ++++
> > > >  arch/riscv/kernel/vmlinux.lds.S     | 10 +++++++++-
> > > >  arch/riscv/mm/init.c                |  6 ++++++
> > > >  arch/riscv/mm/pageattr.c            |  6 ++++++
> > > >  6 files changed, 29 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/arch/riscv/include/asm/sections.h b/arch/riscv/include/asm/sections.h
> > > > index d60802bfafbc..730d2c4a844d 100644
> > > > --- a/arch/riscv/include/asm/sections.h
> > > > +++ b/arch/riscv/include/asm/sections.h
> > > > @@ -10,6 +10,8 @@
> > > >  #include <asm-generic/sections.h>
> > > >  extern char _start[];
> > > >  extern char _start_kernel[];
> > > > +extern char __init_data_begin[], __init_data_end[];
> > > > +extern char __init_text_begin[], __init_text_end[];
> > > >
> > > >  extern bool init_mem_is_free;
> > > >
> > > > diff --git a/arch/riscv/include/asm/set_memory.h b/arch/riscv/include/asm/set_memory.h
> > > > index 4cc3a4e2afd3..913429c9c1ae 100644
> > > > --- a/arch/riscv/include/asm/set_memory.h
> > > > +++ b/arch/riscv/include/asm/set_memory.h
> > > > @@ -15,6 +15,7 @@ int set_memory_ro(unsigned long addr, int numpages);
> > > >  int set_memory_rw(unsigned long addr, int numpages);
> > > >  int set_memory_x(unsigned long addr, int numpages);
> > > >  int set_memory_nx(unsigned long addr, int numpages);
> > > > +int set_memory_default(unsigned long addr, int numpages);
> > > >  void protect_kernel_text_data(void);
> > > >  #else
> > > >  static inline int set_memory_ro(unsigned long addr, int numpages) { return 0; }
> > > > @@ -22,6 +23,7 @@ static inline int set_memory_rw(unsigned long addr, int numpages) { return 0; }
> > > >  static inline int set_memory_x(unsigned long addr, int numpages) { return 0; }
> > > >  static inline int set_memory_nx(unsigned long addr, int numpages) { return 0; }
> > > >  static inline void protect_kernel_text_data(void) {};
> > > > +static inline int set_memory_default(unsigned long addr, int numpages) { return 0; }
> > > >  #endif
> > > >
> > > >  int set_direct_map_invalid_noflush(struct page *page);
> > > > diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> > > > index 4176a2affd1d..b8a35ef0eab0 100644
> > > > --- a/arch/riscv/kernel/setup.c
> > > > +++ b/arch/riscv/kernel/setup.c
> > > > @@ -129,6 +129,10 @@ bool init_mem_is_free = false;
> > > >
> > > >  void free_initmem(void)
> > > >  {
> > > > +       unsigned long init_begin = (unsigned long)__init_begin;
> > > > +       unsigned long init_end = (unsigned long)__init_end;
> > > > +
> > > > +       set_memory_default(init_begin, (init_end - init_begin) >> PAGE_SHIFT);
> > > >         free_initmem_default(POISON_FREE_INITMEM);
> > > >         init_mem_is_free = true;
> > > >  }
> > > > diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
> > > > index 0807633f0dc8..15b9882588ae 100644
> > > > --- a/arch/riscv/kernel/vmlinux.lds.S
> > > > +++ b/arch/riscv/kernel/vmlinux.lds.S
> > > > @@ -30,8 +30,8 @@ SECTIONS
> > > >         . = ALIGN(PAGE_SIZE);
> > > >
> > > >         __init_begin = .;
> > > > +       __init_text_begin = .;
> > > >         INIT_TEXT_SECTION(PAGE_SIZE)
> > > > -       INIT_DATA_SECTION(16)
> > > >         . = ALIGN(8);
> > > >         __soc_early_init_table : {
> > > >                 __soc_early_init_table_start = .;
> > > > @@ -48,11 +48,19 @@ SECTIONS
> > > >         {
> > > >                 EXIT_TEXT
> > > >         }
> > > > +
> > > > +       __init_text_end = .;
> > > > +       . = ALIGN(SECTION_ALIGN);
> > > > +       /* Start of init data section */
> > > > +       __init_data_begin = .;
> > > > +       INIT_DATA_SECTION(16)
> > > >         .exit.data :
> > > >         {
> > > >                 EXIT_DATA
> > > >         }
> > > >         PERCPU_SECTION(L1_CACHE_BYTES)
> > > > +
> > > > +       __init_data_end = .;
> > > >         __init_end = .;
> > > >
> > > >         . = ALIGN(SECTION_ALIGN);
> > > > diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> > > > index 7859a1d1b34d..3ef0eafcc7c7 100644
> > > > --- a/arch/riscv/mm/init.c
> > > > +++ b/arch/riscv/mm/init.c
> > > > @@ -627,11 +627,17 @@ void protect_kernel_text_data(void)
> > > >  {
> > > >         unsigned long text_start = (unsigned long)_text;
> > > >         unsigned long text_end = (unsigned long)_etext;
> > > > +       unsigned long init_text_start = (unsigned long)__init_text_begin;
> > > > +       unsigned long init_text_end = (unsigned long)__init_text_end;
> > > > +       unsigned long init_data_start = (unsigned long)__init_data_begin;
> > > > +       unsigned long init_data_end = (unsigned long)__init_data_end;
> > > >         unsigned long rodata_start = (unsigned long)__start_rodata;
> > > >         unsigned long data_start = (unsigned long)_data;
> > > >         unsigned long max_low = (unsigned long)(__va(PFN_PHYS(max_low_pfn)));
> > > >
> > > > +       set_memory_ro(init_text_start, (init_text_end - init_text_start) >> PAGE_SHIFT);
> > > >         set_memory_ro(text_start, (text_end - text_start) >> PAGE_SHIFT);
> > > > +       set_memory_nx(init_data_start, (init_data_end - init_data_start) >> PAGE_SHIFT);
> > > >         set_memory_nx(rodata_start, (data_start - rodata_start) >> PAGE_SHIFT);
> > > >         set_memory_nx(data_start, (max_low - data_start) >> PAGE_SHIFT);
> > > >  }
> > > > diff --git a/arch/riscv/mm/pageattr.c b/arch/riscv/mm/pageattr.c
> > > > index 19fecb362d81..aecedaf086ab 100644
> > > > --- a/arch/riscv/mm/pageattr.c
> > > > +++ b/arch/riscv/mm/pageattr.c
> > > > @@ -128,6 +128,12 @@ static int __set_memory(unsigned long addr, int numpages, pgprot_t set_mask,
> > > >         return ret;
> > > >  }
> > > >
> > > > +int set_memory_default(unsigned long addr, int numpages)
> > > > +{
> > > > +       return __set_memory(addr, numpages, __pgprot(_PAGE_KERNEL | _PAGE_EXEC),
> > > > +                           __pgprot(0));
> > > > +}
> > > > +
> > > >  int set_memory_ro(unsigned long addr, int numpages)
> > > >  {
> > > >         return __set_memory(addr, numpages, __pgprot(_PAGE_READ),
> > >
> > >
> > > Hi Atish,
> > >
> > > I tested this patchset and CONFIG_DEBUG_WX=y
> > >
> >
> > Thanks for testing the patch.
> >
> > > [    2.664012] Freeing unused kernel memory: 114420K
> > > [    2.666081] ------------[ cut here ]------------
> > > [    2.666779] riscv/mm: Found insecure W+X mapping at address
> > > (____ptrval____)/0xffffffe000000000
> > > [    2.668004] WARNING: CPU: 0 PID: 1 at arch/riscv/mm/ptdump.c:200
> > > note_page+0xc2/0x238
> > > [    2.669147] Modules linked in:
> > > [    2.669735] CPU: 0 PID: 1 Comm: swapper/0 Not tainted
> > > 5.9.0-rc8-00033-gfacf070a80ea #153
> > > [    2.670466] epc: ffffffe00700697c ra : ffffffe00700697c sp : ffffffe0fba9bc10
> > > [    2.671054]  gp : ffffffe007e73078 tp : ffffffe0fba90000 t0 :
> > > ffffffe007e861d0
> > > [    2.671683]  t1 : 0000000000000064 t2 : ffffffe007801664 s0 :
> > > ffffffe0fba9bc60
> > > [    2.672499]  s1 : ffffffe0fba9bde8 a0 : 0000000000000053 a1 :
> > > 0000000000000020
> > > [    2.673119]  a2 : 0000000000000000 a3 : 00000000000000f4 a4 :
> > > d4328dc070ccb100
> > > [    2.673729]  a5 : d4328dc070ccb100 a6 : 0000000000000000 a7 :
> > > ffffffe007851e98
> > > [    2.674333]  s2 : ffffffe007000000 s3 : ffffffe0fba9bde8 s4 :
> > > 0000000087200000
> > > [    2.674963]  s5 : 00000000000000cb s6 : 0000000000000003 s7 :
> > > ffffffe007e7ac00
> > > [    2.675564]  s8 : ffffffe000000000 s9 : ffffffe007000000 s10:
> > > ffffffe000000000
> > > [    2.676392]  s11: ffffffe040000000 t3 : 000000000001da48 t4 :
> > > 000000000001da48
> > > [    2.676992]  t5 : ffffffe007e74490 t6 : ffffffe007e81432
> > > [    2.677449] status: 0000000000000120 badaddr: 0000000000000000
> > > cause: 0000000000000003
> > > [    2.678128] ---[ end trace 5f0a86dbe986db9b ]---
> > > [    2.678952] Checked W+X mappings: failed, 28672 W+X pages found
> > > [    2.679737] Run /init as init process
> > >
> >
> > This would be triggered for the current kernel as well as we don't
> > protect the permission for __init section at all. As you correctly
> > pointed out, __init & .head sections are mapped with same permissions
> > because of 2MB mappings.
> >
> > Currently, the entire head.text & init section have RWX permission.
> > This patch is trying remove the write permission from .init.text &
> > .head.text and execute permission from .init.data until kernel is
> > booted.
> > It doesn't provide full protection but better than the current scheme.
> >
> > To remove the write permission of .head.txt only, we have to keep
> > .head.txt & .init.text section in separate sections. The linear
> > mapping would look like this in that case.
> > There are no issues as such but kernel size would increase by another 2M.
> >
> > ---[ Linear mapping ]---
> > 0xffffffe000000000-0xffffffe000200000    0x0000000080200000         2M
> > PMD     D A . . X . R V
> > 0xffffffe000200000-0xffffffe000600000    0x0000000080400000         4M
> > PMD     D A . . . W R V
> > 0xffffffe000600000-0xffffffe000e00000    0x0000000080800000         8M
> > PMD     D A . . X . R V
> > 0xffffffe000e00000-0xffffffe001400000    0x0000000081000000         6M
> > PMD     D A . . . . R V
> > 0xffffffe001400000-0xffffffe03fe00000    0x0000000081600000      1002M
> > PMD     D A . . . W R V
> >
> > The other solution would be move init section below text. Keep text &
> > head in one section.
> > The .init.text & .init.data will be in separate sections after that.
> > Here is the mapping in that case.
> >
> > ---[ Linear mapping ]---
> > 0xffffffe000000000-0xffffffe000800000    0x0000000080200000         8M
> > PMD     D A . . X . R V
> > 0xffffffe000800000-0xffffffe000c00000    0x0000000080a00000         4M
> > PMD     D A . . . W R V
> > 0xffffffe000c00000-0xffffffe001200000    0x0000000080e00000         6M
> > PMD     D A . . . . R V
> > 0xffffffe001200000-0xffffffe03fe00000    0x0000000081400000      1004M
> > PMD     D A . . . W R V
> >
> > I prefer the 2nd approach compared to the first one as it saves memory
> > and we can fix lockdep issue without adding arch_is_kernel_data
> > to sections.h (Guo's patch).
> >
> > However, the 2nd approach throws this problem if
> > CONFIG_HARDENED_USERCOPY is enabled.
> >
> > net/ipv4/ipconfig.o: in function `ic_setup_routes':
> > /home/atish/workspace/linux/net/ipv4/ipconfig.c:400:(.init.text+0x1c4):
> > relocation truncated to fit: R_RISCV_JAL against symbol `ip_rt_ioctl'
> > defined in .text section in net/ipv4/fib_frontend.o
> > make: *** [Makefile:1162: vmlinux] Error 1
> >
> > I am currently looking into this to understand why R_RISCV_JAL is
> > generated a generic function invocation
> > where auipc + jalr should have been used.
> >
>
> I checked the relocation is is correct 00000000000001d0 R_RISCV_CALL
>    ip_rt_ioctl
> The assembly from objdump also shows a pair of auipc + jalr.
>
> 1d0:       00000097                auipc   ra,0x0
> 1d4:       000080e7                jalr    ra # 1d0 <.LBE348+0x4>
>
> I don't understand why the toolchain is complaining about relocation
> error only when
> CONFIG_HARDENED_USERCOPY is enabled.
>
> Are we seeing some subtle toolchain bug ?
>
"relocation truncated to fit" usually means that the jump address is
too far to jump.
Maybe trying "-mno-relax -Wl,--no-relax" to disable linker relax or
checking if somewhere just using jal instead of call?