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mmu: map device memory as non-executable

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This fixes the random SErrors after returning from a page fault. Turns
out the M1 was randomly deciding to speculate an instruction fetch from
address 0, triggering a fabric error.

Quoting the ARM ARM:

"Hardware does not prevent speculative instruction fetches from a memory
location with any of the Device memory attributes unless the memory
location is also marked as Execute-never for all Exception levels.

This means that to prevent speculative instruction fetches from memory
locations with Device memory attributes, any location that is assigned
any Device memory type must also be marked as execute-never for all
Exception levels. Failure to mark a memory location with any Device
memory attribute as execute-never for all Exception levels is a
programming error."

Signed-off-by: Hector Martin <marcan@marcan.st>
This commit is contained in:
Hector Martin 2021-01-31 13:42:48 +09:00
parent b65e2ca0e4
commit 96d133e854
1 changed files with 18 additions and 8 deletions
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26
src/memory.c
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@ -47,6 +47,14 @@ static inline void write_sctlr(u64 val)
#define PTE_TYPE_TABLE 0b11 #define PTE_TYPE_TABLE 0b11
#define PTE_FLAG_ACCESS (1 << 10) #define PTE_FLAG_ACCESS (1 << 10)
#define PTE_MAIR_INDEX(i) ((i & 7) << 2) #define PTE_MAIR_INDEX(i) ((i & 7) << 2)
#define PTE_PXN (1L << 53)
#define PTE_UXN (1L << 54)
#define PTE_AP_RO (1L << 7)
#define PTE_AP_EL0 (1L << 6)
#define PERM_RO PTE_AP_RO | PTE_PXN | PTE_UXN
#define PERM_RW PTE_PXN | PTE_UXN
#define PERM_RWX 0
/* /*
* https://developer.arm.com/docs/ddi0595/g/aarch64-system-registers/sctlr_el2 * https://developer.arm.com/docs/ddi0595/g/aarch64-system-registers/sctlr_el2
@ -140,12 +148,13 @@ static u64 pagetable_L1[2][ENTRIES_PER_TABLE] ALIGNED(PAGE_SIZE);
static u64 pagetable_L2[MAX_L2_TABLES][ENTRIES_PER_TABLE] ALIGNED(PAGE_SIZE); static u64 pagetable_L2[MAX_L2_TABLES][ENTRIES_PER_TABLE] ALIGNED(PAGE_SIZE);
static u32 pagetable_L2_next = 0; static u32 pagetable_L2_next = 0;
static u64 mmu_make_block_pte(uintptr_t addr, u8 attribute_index) static u64 mmu_make_block_pte(uintptr_t addr, u8 attribute_index, u64 perms)
{ {
u64 pte = PTE_TYPE_BLOCK; u64 pte = PTE_TYPE_BLOCK;
pte |= addr; pte |= addr;
pte |= PTE_FLAG_ACCESS; pte |= PTE_FLAG_ACCESS;
pte |= PTE_MAIR_INDEX(attribute_index); pte |= PTE_MAIR_INDEX(attribute_index);
pte |= perms;
return pte; return pte;
} }
@ -228,7 +237,7 @@ static u64 *mmu_get_L2_table(uintptr_t addr)
return (u64 *)mmu_extract_addr(desc_l1); return (u64 *)mmu_extract_addr(desc_l1);
} }
static void mmu_add_single_mapping(uintptr_t from, uintptr_t to, u8 attribute_index) static void mmu_add_single_mapping(uintptr_t from, uintptr_t to, u8 attribute_index, u64 perms)
{ {
u64 *tbl_l2 = mmu_get_L2_table(from); u64 *tbl_l2 = mmu_get_L2_table(from);
u64 l2_idx = mmu_extract_L2_index(from); u64 l2_idx = mmu_extract_L2_index(from);
@ -236,10 +245,11 @@ static void mmu_add_single_mapping(uintptr_t from, uintptr_t to, u8 attribute_in
if (tbl_l2[l2_idx]) if (tbl_l2[l2_idx])
panic("MMU: mapping for %lx already exists", from); panic("MMU: mapping for %lx already exists", from);
tbl_l2[l2_idx] = mmu_make_block_pte(to, attribute_index); tbl_l2[l2_idx] = mmu_make_block_pte(to, attribute_index, perms);
} }
static void mmu_add_mapping(uintptr_t from, uintptr_t to, size_t size, u8 attribute_index) static void mmu_add_mapping(uintptr_t from, uintptr_t to, size_t size, u8 attribute_index,
u64 perms)
{ {
if (from % L2_PAGE_SIZE) if (from % L2_PAGE_SIZE)
panic("mmu_add_mapping: from address not aligned: %lx", from); panic("mmu_add_mapping: from address not aligned: %lx", from);
@ -249,7 +259,7 @@ static void mmu_add_mapping(uintptr_t from, uintptr_t to, size_t size, u8 attrib
panic("mmu_add_mapping: size not aligned: %lx", size); panic("mmu_add_mapping: size not aligned: %lx", size);
while (size > 0) { while (size > 0) {
mmu_add_single_mapping(from, to, attribute_index); mmu_add_single_mapping(from, to, attribute_index, perms);
from += L2_PAGE_SIZE; from += L2_PAGE_SIZE;
to += L2_PAGE_SIZE; to += L2_PAGE_SIZE;
size -= L2_PAGE_SIZE; size -= L2_PAGE_SIZE;
@ -262,14 +272,14 @@ static void mmu_add_default_mappings(void)
* create MMIO mapping as both nGnRnE (identity) and nGnRE (starting at * create MMIO mapping as both nGnRnE (identity) and nGnRE (starting at
* 0xf0_0000_0000) * 0xf0_0000_0000)
*/ */
mmu_add_mapping(0x0000000000, 0x0000000000, 0x0800000000, MAIR_INDEX_DEVICE_nGnRnE); mmu_add_mapping(0x0000000000, 0x0000000000, 0x0800000000, MAIR_INDEX_DEVICE_nGnRnE, PERM_RW);
mmu_add_mapping(0xf000000000, 0x0000000000, 0x0800000000, MAIR_INDEX_DEVICE_nGnRE); mmu_add_mapping(0xf000000000, 0x0000000000, 0x0800000000, MAIR_INDEX_DEVICE_nGnRE, PERM_RW);
/* /*
* create identity mapping for 16GB RAM from 0x08_0000_0000 to * create identity mapping for 16GB RAM from 0x08_0000_0000 to
* 0x0c_0000_0000 * 0x0c_0000_0000
*/ */
mmu_add_mapping(0x0800000000, 0x0800000000, 0x0400000000, MAIR_INDEX_NORMAL); mmu_add_mapping(0x0800000000, 0x0800000000, 0x0400000000, MAIR_INDEX_NORMAL, PERM_RWX);
} }
static void mmu_configure(void) static void mmu_configure(void)