[PATCH 6/8] x86/boot: Setup memory protection for bzImage code

Evgeniy Baskov
2022-08-01T16:39:40Z

Use previously added code to use 4KB pages for mapping. Map compressed
and uncompressed kernel with appropriate memory protection attributes.
For compressed kernel set them up manually. For uncompressed kernel
used flags specified in ELF header.

Move 'boot/compressed/pgtable.h' to common headers to make it accessible
from EFISTUB code.

Signed-off-by: Evgeniy Baskov <baskov@ispras.ru>

delete mode 100644 arch/x86/boot/compressed/pgtable.h
create mode 100644 arch/x86/include/asm/shared/pgtable.h

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 5273367283b7..4cc1463b98e8 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -35,7 +35,7 @@
#include <asm/bootparam.h>
#include <asm/desc_defs.h>
#include <asm/trapnr.h>
-#include "pgtable.h"
+#include <asm/shared/pgtable.h>

/*
* Locally defined symbols should be marked hidden:
diff --git a/arch/x86/boot/compressed/ident_map_64.c b/arch/x86/boot/compressed/ident_map_64.c
index d4a314cc50d6..04022c080114 100644
--- a/arch/x86/boot/compressed/ident_map_64.c
+++ b/arch/x86/boot/compressed/ident_map_64.c
@@ -28,6 +28,7 @@
#include <asm/trap_pf.h>
#include <asm/trapnr.h>
#include <asm/init.h>
+#include <asm/shared/pgtable.h>
/* Use the static base for this part of the boot process */
#undef __PAGE_OFFSET
#define __PAGE_OFFSET __PAGE_OFFSET_BASE
@@ -86,24 +87,45 @@ phys_addr_t physical_mask = (1ULL << __PHYSICAL_MASK_SHIFT) - 1;
* Due to relocation, pointers must be assigned at run time not build time.
*/
static struct x86_mapping_info mapping_info;
+static bool has_nx;

/*
* Adds the specified range to the identity mappings.
*/
-void kernel_add_identity_map(unsigned long start, unsigned long end)
+unsigned long kernel_add_identity_map(unsigned long start,
+ unsigned long end,
+ unsigned int flags)
{
int ret;

/* Align boundary to 2M. */
- start = round_down(start, PMD_SIZE);
- end = round_up(end, PMD_SIZE);
+ start = round_down(start, PAGE_SIZE);
+ end = round_up(end, PAGE_SIZE);
if (start >= end)
- return;
+ return start;
+
+ /* Enforce W^X -- just stop booting with error on violation. */
+ if ((flags & (MAP_EXEC | MAP_WRITE)) == (MAP_EXEC | MAP_WRITE))
+ error("Error: W^X violation\n");
+
+ bool nx = !(flags & MAP_EXEC) && has_nx;
+ bool ro = !(flags & MAP_WRITE);
+
+ mapping_info.page_flag = sme_me_mask | (nx ?
+ (ro ? __PAGE_KERNEL_RO : __PAGE_KERNEL) :
+ (ro ? __PAGE_KERNEL_ROX : __PAGE_KERNEL_EXEC));

/* Build the mapping. */
- ret = kernel_ident_mapping_init(&mapping_info, (pgd_t *)top_level_pgt, start, end);
+ ret = kernel_ident_mapping_init(&mapping_info,
+ (pgd_t *)top_level_pgt,
+ start, end);
if (ret)
error("Error: kernel_ident_mapping_init() failed\n");
+
+ if (!(flags & MAP_NOFLUSH))
+ write_cr3(top_level_pgt);
+
+ return start;
}

/* Locates and clears a region for a new top level page table. */
@@ -112,14 +134,17 @@ void initialize_identity_maps(void *rmode)
unsigned long cmdline;
struct setup_data *sd;

+ boot_params = rmode;
+
/* Exclude the encryption mask from __PHYSICAL_MASK */
physical_mask &= ~sme_me_mask;

/* Init mapping_info with run-time function/buffer pointers. */
mapping_info.alloc_pgt_page = alloc_pgt_page;
mapping_info.context = &pgt_data;
- mapping_info.page_flag = __PAGE_KERNEL_LARGE_EXEC | sme_me_mask;
+ mapping_info.page_flag = __PAGE_KERNEL_EXEC | sme_me_mask;
mapping_info.kernpg_flag = _KERNPG_TABLE;
+ mapping_info.allow_4kpages = 1;

/*
* It should be impossible for this not to already be true,
@@ -151,18 +176,46 @@ void initialize_identity_maps(void *rmode)
top_level_pgt = (unsigned long)alloc_pgt_page(&pgt_data);
}

+ /*
+ * Check if this CPU supports NX flag and use
+ * it appropriately for identity mappings.
+ */
+
+ has_nx = native_cpuid_edx(0x80000001) & (1 << 20);
+ if (!has_nx)
+ debug_putstr("NX bit is not supported.\n");
+
/*
* New page-table is set up - map the kernel image, boot_params and the
* command line. The uncompressed kernel requires boot_params and the
- * command line to be mapped in the identity mapping. Map them
- * explicitly here in case the compressed kernel does not touch them,
- * or does not touch all the pages covering them.
+ * command line to be mapped in the identity mapping.
+ * Every other accessed memory region is mapped later, if required.
*/
- kernel_add_identity_map((unsigned long)_head, (unsigned long)_end);
- boot_params = rmode;
- kernel_add_identity_map((unsigned long)boot_params, (unsigned long)(boot_params + 1));
+ extern char _head[], _ehead[];
+ kernel_add_identity_map((unsigned long)_head,
+ (unsigned long)_ehead, MAP_EXEC | MAP_NOFLUSH);
+
+ extern char _compressed[], _ecompressed[];
+ kernel_add_identity_map((unsigned long)_compressed,
+ (unsigned long)_ecompressed, MAP_WRITE | MAP_NOFLUSH);
+
+ extern char _text[], _etext[];
+ kernel_add_identity_map((unsigned long)_text,
+ (unsigned long)_etext, MAP_EXEC | MAP_NOFLUSH);
+
+ extern char _rodata[], _erodata[];
+ kernel_add_identity_map((unsigned long)_rodata,
+ (unsigned long)_erodata, MAP_NOFLUSH);
+
+ extern char _data[], _end[];
+ kernel_add_identity_map((unsigned long)_data,
+ (unsigned long)_end, MAP_WRITE | MAP_NOFLUSH);
+
+ kernel_add_identity_map((unsigned long)boot_params,
+ (unsigned long)(boot_params + 1), MAP_WRITE | MAP_NOFLUSH);
+
cmdline = get_cmd_line_ptr();
- kernel_add_identity_map(cmdline, cmdline + COMMAND_LINE_SIZE);
+ kernel_add_identity_map(cmdline, cmdline + COMMAND_LINE_SIZE, MAP_NOFLUSH);

/*
* Also map the setup_data entries passed via boot_params in case they
@@ -172,7 +225,7 @@ void initialize_identity_maps(void *rmode)
while (sd) {
unsigned long sd_addr = (unsigned long)sd;

- kernel_add_identity_map(sd_addr, sd_addr + sizeof(*sd) + sd->len);
+ kernel_add_identity_map(sd_addr, sd_addr + sizeof(*sd) + sd->len, MAP_NOFLUSH);
sd = (struct setup_data *)sd->next;
}

@@ -185,26 +238,11 @@ void initialize_identity_maps(void *rmode)
static pte_t *split_large_pmd(struct x86_mapping_info *info,
pmd_t *pmdp, unsigned long __address)
{
- unsigned long page_flags;
- unsigned long address;
- pte_t *pte;
- pmd_t pmd;
- int i;
-
- pte = (pte_t *)info->alloc_pgt_page(info->context);
+ unsigned long address = __address & PMD_MASK;
+ pte_t *pte = ident_split_large_pmd(info, pmdp, address);
if (!pte)
return NULL;

- address = __address & PMD_MASK;
- /* No large page - clear PSE flag */
- page_flags = info->page_flag & ~_PAGE_PSE;
-
- /* Populate the PTEs */
- for (i = 0; i < PTRS_PER_PMD; i++) {
- set_pte(&pte[i], __pte(address | page_flags));
- address += PAGE_SIZE;
- }
-
/*
* Ideally we need to clear the large PMD first and do a TLB
* flush before we write the new PMD. But the 2M range of the
@@ -214,7 +252,7 @@ static pte_t *split_large_pmd(struct x86_mapping_info *info,
* also the only user of the page-table, so there is no chance
* of a TLB multihit.
*/
- pmd = __pmd((unsigned long)pte | info->kernpg_flag);
+ pmd_t pmd = __pmd((unsigned long)pte | info->kernpg_flag);
set_pmd(pmdp, pmd);
/* Flush TLB to establish the new PMD */
write_cr3(top_level_pgt);
@@ -377,5 +415,5 @@ void do_boot_page_fault(struct pt_regs *regs, unsigned long error_code)
* Error code is sane - now identity map the 2M region around
* the faulting address.
*/
- kernel_add_identity_map(address, end);
+ kernel_add_identity_map(address, end, MAP_WRITE);
}
diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index cf690d8712f4..49f6cc7a7bde 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -14,10 +14,10 @@

#include "misc.h"
#include "error.h"
-#include "pgtable.h"
#include "../string.h"
#include "../voffset.h"
#include <asm/bootparam_utils.h>
+#include <asm/shared/pgtable.h>

/*
* WARNING!!
@@ -277,7 +277,8 @@ static inline void handle_relocations(void *output, unsigned long output_len,
{ }
#endif

-static void parse_elf(void *output)
+static void parse_elf(void *output, unsigned long output_len,
+ unsigned long virt_addr)
{
#ifdef CONFIG_X86_64
Elf64_Ehdr ehdr;
@@ -287,6 +288,7 @@ static void parse_elf(void *output)
Elf32_Phdr *phdrs, *phdr;
#endif
void *dest;
+ unsigned long addr;
int i;

memcpy(&ehdr, output, sizeof(ehdr));
@@ -323,7 +325,43 @@ static void parse_elf(void *output)
#endif
memmove(dest, output + phdr->p_offset, phdr->p_filesz);
break;
- default: /* Ignore other PT_* */ break;
+ default:
+ /* Ignore other PT_* */
+ break;
+ }
+ }
+
+ handle_relocations(output, output_len, virt_addr);
+
+ for (i = 0; i < ehdr.e_phnum; i++) {
+ phdr = &phdrs[i];
+
+ switch (phdr->p_type) {
+ case PT_LOAD:
+#ifdef CONFIG_RELOCATABLE
+ addr = (unsigned long)output;
+ addr += (phdr->p_paddr - LOAD_PHYSICAL_ADDR);
+#else
+ addr = phdr->p_paddr;
+#endif
+ /*
+ * Simultaneously readable and writable segments are
+ * violating W^X, and should not be present in vmlinux image.
+ */
+ if ((phdr->p_flags & (PF_X | PF_W)) == (PF_X | PF_W))
+ error("W^X violation for ELF segment");
+
+ unsigned int flags = MAP_PROTECT;
+ if (phdr->p_flags & PF_X)
+ flags |= MAP_EXEC;
+ if (phdr->p_flags & PF_W)
+ flags |= MAP_WRITE;
+
+ kernel_add_identity_map(addr, addr + phdr->p_memsz, flags);
+ break;
+ default:
+ /* Ignore other PT_* */
+ break;
}
}

@@ -434,6 +472,11 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
needed_size,
&virt_addr);

+ unsigned long phys_addr = (unsigned long)output;
+ output = (unsigned char *)kernel_add_identity_map(phys_addr,
+ phys_addr + needed_size,
+ MAP_ALLOC | MAP_WRITE);
+
/* Validate memory location choices. */
if ((unsigned long)output & (MIN_KERNEL_ALIGN - 1))
error("Destination physical address inappropriately aligned");
@@ -456,8 +499,7 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
debug_putstr("\nDecompressing Linux... ");
__decompress(input_data, input_len, NULL, NULL, output, output_len,
NULL, error);
- parse_elf(output);
- handle_relocations(output, output_len, virt_addr);
+ parse_elf(output, output_len, virt_addr);
debug_putstr("done.\nBooting the kernel.\n");

/* Disable exception handling before booting the kernel */
diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index 4910bf230d7b..699b87b7813a 100644
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -161,8 +161,20 @@ static inline int count_immovable_mem_regions(void) { return 0; }
#ifdef CONFIG_X86_5LEVEL
extern unsigned int __pgtable_l5_enabled, pgdir_shift, ptrs_per_p4d;
#endif
-extern void kernel_add_identity_map(unsigned long start, unsigned long end);
-
+#ifdef CONFIG_X86_64
+extern unsigned long kernel_add_identity_map(unsigned long start,
+ unsigned long end,
+ unsigned int flags);
+#else
+static inline unsigned long kernel_add_identity_map(unsigned long start,
+ unsigned long end,
+ unsigned int flags)
+{
+ (void)flags;
+ (void)end;
+ return start;
+}
+#endif
/* Used by PAGE_KERN* macros: */
extern pteval_t __default_kernel_pte_mask;

diff --git a/arch/x86/boot/compressed/pgtable.h b/arch/x86/boot/compressed/pgtable.h
deleted file mode 100644
index cc9b2529a086..000000000000
--- a/arch/x86/boot/compressed/pgtable.h
+++ /dev/null
@@ -1,20 +0,0 @@
-#ifndef BOOT_COMPRESSED_PAGETABLE_H
-#define BOOT_COMPRESSED_PAGETABLE_H
-
-#define TRAMPOLINE_32BIT_SIZE (2 * PAGE_SIZE)
-
-#define TRAMPOLINE_32BIT_PGTABLE_OFFSET 0
-
-#define TRAMPOLINE_32BIT_CODE_OFFSET PAGE_SIZE
-#define TRAMPOLINE_32BIT_CODE_SIZE 0x80
-
-#define TRAMPOLINE_32BIT_STACK_END TRAMPOLINE_32BIT_SIZE
-
-#ifndef __ASSEMBLER__
-
-extern unsigned long *trampoline_32bit;
-
-extern void trampoline_32bit_src(void *return_ptr);
-
-#endif /* __ASSEMBLER__ */
-#endif /* BOOT_COMPRESSED_PAGETABLE_H */
diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c
index 2ac12ff4111b..c7cf5a1059a8 100644
--- a/arch/x86/boot/compressed/pgtable_64.c
+++ b/arch/x86/boot/compressed/pgtable_64.c
@@ -2,7 +2,7 @@
#include "misc.h"
#include <asm/e820/types.h>
#include <asm/processor.h>
-#include "pgtable.h"
+#include <asm/shared/pgtable.h>
#include "../string.h"
#include "efi.h"

diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index 52f989f6acc2..82a10395cf22 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -13,6 +13,7 @@
#include "misc.h"

#include <asm/pgtable_types.h>
+#include <asm/shared/pgtable.h>
#include <asm/sev.h>
#include <asm/trapnr.h>
#include <asm/trap_pf.h>
@@ -427,10 +428,11 @@ void sev_prep_identity_maps(unsigned long top_level_pgt)
unsigned long cc_info_pa = boot_params->cc_blob_address;
struct cc_blob_sev_info *cc_info;

- kernel_add_identity_map(cc_info_pa, cc_info_pa + sizeof(*cc_info));
+ kernel_add_identity_map(cc_info_pa, cc_info_pa + sizeof(*cc_info), MAP_NOFLUSH);

cc_info = (struct cc_blob_sev_info *)cc_info_pa;
- kernel_add_identity_map(cc_info->cpuid_phys, cc_info->cpuid_phys + cc_info->cpuid_len);
+ kernel_add_identity_map(cc_info->cpuid_phys,
+ cc_info->cpuid_phys + cc_info->cpuid_len, MAP_NOFLUSH);
}

sev_verify_cbit(top_level_pgt);
diff --git a/arch/x86/include/asm/shared/pgtable.h b/arch/x86/include/asm/shared/pgtable.h
new file mode 100644
index 000000000000..6527dadf39d6
--- /dev/null
+++ b/arch/x86/include/asm/shared/pgtable.h
@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef ASM_SHARED_PAGETABLE_H
+#define ASM_SHARED_PAGETABLE_H
+
+/* Boot time memory mapping flags used in compressed kernel */
+#define MAP_WRITE 0x02 /* Writable memory */
+#define MAP_EXEC 0x04 /* Executable memory */
+#define MAP_ALLOC 0x10 /* Range needs to be allocated */
+#define MAP_PROTECT 0x20 /* Set exact memory attributes for memory range */
+#define MAP_NOFLUSH 0x40 /* Avoid flushing TLB */
+
+#define TRAMPOLINE_32BIT_SIZE (3 * PAGE_SIZE)
+
+#define TRAMPOLINE_32BIT_PLACEMENT_MAX (0xA0000)
+
+#define TRAMPOLINE_32BIT_PGTABLE_OFFSET 0
+
+#define TRAMPOLINE_32BIT_CODE_OFFSET PAGE_SIZE
+#define TRAMPOLINE_32BIT_CODE_SIZE 0x80
+
+#define TRAMPOLINE_32BIT_STACK_END TRAMPOLINE_32BIT_SIZE
+
+#ifndef __ASSEMBLER__
+
+extern unsigned long *trampoline_32bit;
+
+extern void trampoline_32bit_src(void *return_ptr);
+
+#endif /* __ASSEMBLER__ */
+#endif /* ASM_SHARED_PAGETABLE_H */
--
2.35.1