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

From: Greentime Hu
Date: Mon Oct 12 2020 - 09:15:07 EST

Next message: henrik.bjoernlund@xxxxxxxxxxxxx: "Re: [PATCH net-next v4 02/10] bridge: cfm: Add BRIDGE_CFM to Kconfig."
Previous message: henrik.bjoernlund@xxxxxxxxxxxxx: "Re: [PATCH net-next v4 03/10] bridge: uapi: cfm: Added EtherType used by the CFM protocol."
In reply to: Atish Patra: "[PATCH 4/5] RISC-V: Protect .init.text & .init.data"
Next in thread: Atish Patra: "Re: [PATCH 4/5] RISC-V: Protect .init.text & .init.data"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

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

[ 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

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?

Next message: henrik.bjoernlund@xxxxxxxxxxxxx: "Re: [PATCH net-next v4 02/10] bridge: cfm: Add BRIDGE_CFM to Kconfig."
Previous message: henrik.bjoernlund@xxxxxxxxxxxxx: "Re: [PATCH net-next v4 03/10] bridge: uapi: cfm: Added EtherType used by the CFM protocol."
In reply to: Atish Patra: "[PATCH 4/5] RISC-V: Protect .init.text & .init.data"
Next in thread: Atish Patra: "Re: [PATCH 4/5] RISC-V: Protect .init.text & .init.data"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]