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

From: Atish Patra
Date: Mon Oct 12 2020 - 22:42:04 EST

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On Mon, Oct 12, 2020 at 4:26 PM Atish Patra <atishp@xxxxxxxxxxxxxx> wrote:
>
> On Mon, Oct 12, 2020 at 6:15 AM Greentime Hu <greentime.hu@xxxxxxxxxx> wrote:
> >
> > Atish Patra <atish.patra@xxxxxxx> 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@xxxxxxx>
> > > ---
> > > 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 ?

> > After debugging, I found it is because
> > set_memory_ro()/set_memory_nx()/... can't handle the 4KB-aligned
> > address if it is a 2MB mapping address.
> > For example, if we gave 0xffffffe000001000 and this address is in a
> > PMD mapping which is 2MB mapping, it will set the page attributes from
> > 0xffffffe000000000.
> > And this caused the CPU hotplug failed because it is in head.text section.
> >
> > #0 pageattr_pmd_entry (pmd=0xffffffe0ffdff000,
> > addr=18446743936270602240, next=18446743936270766080,
> > walk=0xffffffe007e03e98) at arch/riscv/mm/pageattr.c:70
> > 70 pmd_t val = READ_ONCE(*pmd);
> > => 0xffffffe007005e96 <pageattr_pmd_entry+0>: 41 11 addi sp,sp,-16
> > 0xffffffe007005e98 <pageattr_pmd_entry+2>: 22 e4 sd s0,8(sp)
> > 0xffffffe007005e9a <pageattr_pmd_entry+4>: 00 08 addi s0,sp,16
> > 0xffffffe007005e9c <pageattr_pmd_entry+6>: 1c 61 ld a5,0(a0)
> > (gdb) p/x addr
> > $21 = 0xffffffe000001000
> >
> > # cat /sys/kernel/debug/kernel_page_tables
> > ---[ Fixmap start ]---
> > 0xffffffcefef00000-0xffffffceff000000 0x0000000082200000 1M
> > PTE D A . . . W R V
> > ---[ Fixmap end ]---
> > ---[ PCI I/O start ]---
> > ---[ PCI I/O end ]---
> > ---[ vmalloc() area ]---
> > 0xffffffd000090000-0xffffffd000093000 0x00000001741bb000 12K
> > PTE D A . . . W R V
> > 0xffffffdffffbb000-0xffffffdffffbe000 0x0000000175f97000 12K
> > PTE D A . . . W R V
> > 0xffffffdffffcc000-0xffffffdffffcf000 0x0000000175f9a000 12K
> > PTE D A . . . W R V
> > 0xffffffdffffdd000-0xffffffdffffe0000 0x0000000175f9d000 12K
> > PTE D A . . . W R V
> > 0xffffffdffffee000-0xffffffdfffff1000 0x0000000175fa0000 12K
> > PTE D A . . . W R V
> > ---[ vmalloc() end ]---
> > ---[ Linear mapping ]---
> > 0xffffffe000000000-0xffffffe007000000 0x0000000080200000 112M
> > PMD D A . . X W R V
> > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > 0xffffffe007000000-0xffffffe007800000 0x0000000087200000 8M
> > PMD D A . . X . R V
> > 0xffffffe007800000-0xffffffe007e00000 0x0000000087a00000 6M
> > PMD D A . . . . R V
> > 0xffffffe007e00000-0xffffffe0ffe00000 0x0000000088000000 3968M
> > PMD D A . . . W R V
> > #
> >
> > Any idea?
> >
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@xxxxxxxxxxxxxxxxxxx
> > http://lists.infradead.org/mailman/listinfo/linux-riscv
>
>
>
> --
> Regards,
> Atish

--
Regards,
Atish

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