powerpc/mm/32s: Use BATs for STRICT_KERNEL_RWX

Today, STRICT_KERNEL_RWX is based on the use of regular pages
to map kernel pages.

On Book3s 32, it has three consequences:
- Using pages instead of BAT for mapping kernel linear memory severely
impacts performance.
- Exec protection is not effective because no-execute cannot be set at
page level (except on 603 which doesn't have hash tables)
- Write protection is not effective because PP bits do not provide RO
mode for kernel-only pages (except on 603 which handles it in software
via PAGE_DIRTY)

On the 603+, we have:
- Independent IBAT and DBAT allowing limitation of exec parts.
- NX bit can be set in segment registers to forbit execution on memory
mapped by pages.
- RO mode on DBATs even for kernel-only blocks.

On the 601, there is nothing much we can do other than warn the user
about it, because:
- BATs are common to instructions and data.
- BAT do not provide RO mode for kernel-only blocks.
- segment registers don't have the NX bit.

In order to use IBAT for exec protection, this patch:
- Aligns _etext to BAT block sizes (128kb)
- Set NX bit in kernel segment register (Except on vmalloc area when
CONFIG_MODULES is selected)
- Maps kernel text with IBATs.

In order to use DBAT for exec protection, this patch:
- Aligns RW DATA to BAT block sizes (4M)
- Maps kernel RO area with write prohibited DBATs
- Maps remaining memory with remaining DBATs

Here is what we get with this patch on a 832x when activating
STRICT_KERNEL_RWX:

Symbols:
c0000000 T _stext
c0680000 R __start_rodata
c0680000 R _etext
c0800000 T __init_begin
c0800000 T _sinittext

~# cat /sys/kernel/debug/block_address_translation
---[ Instruction Block Address Translation ]---
0: 0xc0000000-0xc03fffff 0x00000000 Kernel EXEC coherent
1: 0xc0400000-0xc05fffff 0x00400000 Kernel EXEC coherent
2: 0xc0600000-0xc067ffff 0x00600000 Kernel EXEC coherent
3:         -
4:         -
5:         -
6:         -
7:         -

---[ Data Block Address Translation ]---
0: 0xc0000000-0xc07fffff 0x00000000 Kernel RO coherent
1: 0xc0800000-0xc0ffffff 0x00800000 Kernel RW coherent
2: 0xc1000000-0xc1ffffff 0x01000000 Kernel RW coherent
3: 0xc2000000-0xc3ffffff 0x02000000 Kernel RW coherent
4: 0xc4000000-0xc7ffffff 0x04000000 Kernel RW coherent
5: 0xc8000000-0xcfffffff 0x08000000 Kernel RW coherent
6: 0xd0000000-0xdfffffff 0x10000000 Kernel RW coherent
7:         -

~# cat /sys/kernel/debug/segment_registers
---[ User Segments ]---
0x00000000-0x0fffffff Kern key 1 User key 1 VSID 0xa085d0
0x10000000-0x1fffffff Kern key 1 User key 1 VSID 0xa086e1
0x20000000-0x2fffffff Kern key 1 User key 1 VSID 0xa087f2
0x30000000-0x3fffffff Kern key 1 User key 1 VSID 0xa08903
0x40000000-0x4fffffff Kern key 1 User key 1 VSID 0xa08a14
0x50000000-0x5fffffff Kern key 1 User key 1 VSID 0xa08b25
0x60000000-0x6fffffff Kern key 1 User key 1 VSID 0xa08c36
0x70000000-0x7fffffff Kern key 1 User key 1 VSID 0xa08d47
0x80000000-0x8fffffff Kern key 1 User key 1 VSID 0xa08e58
0x90000000-0x9fffffff Kern key 1 User key 1 VSID 0xa08f69
0xa0000000-0xafffffff Kern key 1 User key 1 VSID 0xa0907a
0xb0000000-0xbfffffff Kern key 1 User key 1 VSID 0xa0918b

---[ Kernel Segments ]---
0xc0000000-0xcfffffff Kern key 0 User key 1 No Exec VSID 0x000ccc
0xd0000000-0xdfffffff Kern key 0 User key 1 No Exec VSID 0x000ddd
0xe0000000-0xefffffff Kern key 0 User key 1 No Exec VSID 0x000eee
0xf0000000-0xffffffff Kern key 0 User key 1 No Exec VSID 0x000fff

Aligning _etext to 128kb allows to map up to 32Mb text with 8 IBATs:
16Mb + 8Mb + 4Mb + 2Mb + 1Mb + 512kb + 256kb + 128kb (+ 128kb) = 32Mb
(A 9th IBAT is unneeded as 32Mb would need only a single 32Mb block)

Aligning data to 4M allows to map up to 512Mb data with 8 DBATs:
16Mb + 8Mb + 4Mb + 4Mb + 32Mb + 64Mb + 128Mb + 256Mb = 512Mb

Because some processors only have 4 BATs and because some targets need
DBATs for mapping other areas, the following patch will allow to
modify _etext and data alignment.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Christophe Leroy 2019-02-21 19:08:49 +00:00 committed by Michael Ellerman
parent 5e04ae85fb
commit 63b2bc6195
6 changed files with 112 additions and 10 deletions

View File

@ -723,11 +723,13 @@ config THREAD_SHIFT
config ETEXT_SHIFT
int
default 17 if STRICT_KERNEL_RWX && PPC_BOOK3S_32
default PPC_PAGE_SHIFT
config DATA_SHIFT
int
default 24 if STRICT_KERNEL_RWX && PPC64
default 22 if STRICT_KERNEL_RWX && PPC_BOOK3S_32
default PPC_PAGE_SHIFT
config FORCE_MAX_ZONEORDER

View File

@ -174,7 +174,18 @@ static inline bool pte_user(pte_t pte)
* of RAM. -- Cort
*/
#define VMALLOC_OFFSET (0x1000000) /* 16M */
/*
* With CONFIG_STRICT_KERNEL_RWX, kernel segments are set NX. But when modules
* are used, NX cannot be set on VMALLOC space. So vmalloc VM space and linear
* memory shall not share segments.
*/
#if defined(CONFIG_STRICT_KERNEL_RWX) && defined(CONFIG_MODULES)
#define VMALLOC_START ((_ALIGN((long)high_memory, 256L << 20) + VMALLOC_OFFSET) & \
~(VMALLOC_OFFSET - 1))
#else
#define VMALLOC_START ((((long)high_memory + VMALLOC_OFFSET) & ~(VMALLOC_OFFSET-1)))
#endif
#define VMALLOC_END ioremap_bot
#ifndef __ASSEMBLY__

View File

@ -108,11 +108,9 @@ static void __init MMU_setup(void)
__map_without_bats = 1;
__map_without_ltlbs = 1;
}
if (strict_kernel_rwx_enabled()) {
__map_without_bats = 1;
if (strict_kernel_rwx_enabled())
__map_without_ltlbs = 1;
}
}
/*
* MMU_init sets up the basic memory mappings for the kernel,

View File

@ -165,3 +165,11 @@ unsigned long p_block_mapped(phys_addr_t pa);
static inline phys_addr_t v_block_mapped(unsigned long va) { return 0; }
static inline unsigned long p_block_mapped(phys_addr_t pa) { return 0; }
#endif
#if defined(CONFIG_PPC_BOOK3S_32)
void mmu_mark_initmem_nx(void);
void mmu_mark_rodata_ro(void);
#else
static inline void mmu_mark_initmem_nx(void) { }
static inline void mmu_mark_rodata_ro(void) { }
#endif

View File

@ -353,6 +353,9 @@ void mark_initmem_nx(void)
unsigned long numpages = PFN_UP((unsigned long)_einittext) -
PFN_DOWN((unsigned long)_sinittext);
if (v_block_mapped((unsigned long)_stext) + 1)
mmu_mark_initmem_nx();
else
change_page_attr(page, numpages, PAGE_KERNEL);
}
@ -362,6 +365,11 @@ void mark_rodata_ro(void)
struct page *page;
unsigned long numpages;
if (v_block_mapped((unsigned long)_sinittext)) {
mmu_mark_rodata_ro();
return;
}
page = virt_to_page(_stext);
numpages = PFN_UP((unsigned long)_etext) -
PFN_DOWN((unsigned long)_stext);

View File

@ -32,6 +32,7 @@
#include <asm/mmu.h>
#include <asm/machdep.h>
#include <asm/code-patching.h>
#include <asm/sections.h>
#include "mmu_decl.h"
@ -138,15 +139,10 @@ static void clearibat(int index)
bat[0].batl = 0;
}
unsigned long __init mmu_mapin_ram(unsigned long base, unsigned long top)
static unsigned long __init __mmu_mapin_ram(unsigned long base, unsigned long top)
{
int idx;
if (__map_without_bats) {
printk(KERN_DEBUG "RAM mapped without BATs\n");
return base;
}
while ((idx = find_free_bat()) != -1 && base != top) {
unsigned int size = block_size(base, top);
@ -159,6 +155,85 @@ unsigned long __init mmu_mapin_ram(unsigned long base, unsigned long top)
return base;
}
unsigned long __init mmu_mapin_ram(unsigned long base, unsigned long top)
{
int done;
unsigned long border = (unsigned long)__init_begin - PAGE_OFFSET;
if (__map_without_bats) {
pr_debug("RAM mapped without BATs\n");
return base;
}
if (!strict_kernel_rwx_enabled() || base >= border || top <= border)
return __mmu_mapin_ram(base, top);
done = __mmu_mapin_ram(base, border);
if (done != border - base)
return done;
return done + __mmu_mapin_ram(border, top);
}
void mmu_mark_initmem_nx(void)
{
int nb = mmu_has_feature(MMU_FTR_USE_HIGH_BATS) ? 8 : 4;
int i;
unsigned long base = (unsigned long)_stext - PAGE_OFFSET;
unsigned long top = (unsigned long)_etext - PAGE_OFFSET;
unsigned long size;
if (cpu_has_feature(CPU_FTR_601))
return;
for (i = 0; i < nb - 1 && base < top && top - base > (128 << 10);) {
size = block_size(base, top);
setibat(i++, PAGE_OFFSET + base, base, size, PAGE_KERNEL_TEXT);
base += size;
}
if (base < top) {
size = block_size(base, top);
size = max(size, 128UL << 10);
if ((top - base) > size) {
if (strict_kernel_rwx_enabled())
pr_warn("Kernel _etext not properly aligned\n");
size <<= 1;
}
setibat(i++, PAGE_OFFSET + base, base, size, PAGE_KERNEL_TEXT);
base += size;
}
for (; i < nb; i++)
clearibat(i);
update_bats();
for (i = TASK_SIZE >> 28; i < 16; i++) {
/* Do not set NX on VM space for modules */
if (IS_ENABLED(CONFIG_MODULES) &&
(VMALLOC_START & 0xf0000000) == i << 28)
break;
mtsrin(mfsrin(i << 28) | 0x10000000, i << 28);
}
}
void mmu_mark_rodata_ro(void)
{
int nb = mmu_has_feature(MMU_FTR_USE_HIGH_BATS) ? 8 : 4;
int i;
if (cpu_has_feature(CPU_FTR_601))
return;
for (i = 0; i < nb; i++) {
struct ppc_bat *bat = BATS[i];
if (bat_addrs[i].start < (unsigned long)__init_begin)
bat[1].batl = (bat[1].batl & ~BPP_RW) | BPP_RX;
}
update_bats();
}
/*
* Set up one of the I/D BAT (block address translation) register pairs.
* The parameters are not checked; in particular size must be a power