[Crash-utility] [PATH v4 1/2] arm64: fix kernel memory map handling for kaslr-enabled kernel

Monday, 30 May 2016

In kernel v4.6, Kernel ASLR (KASLR) is supported on arm64, and the start
address of the kernel image can be randomized if CONFIG_RANDOMIZE_BASE is
enabled.
Even worse, the kernel image is no more mapped in the linear mapping, but
in vmalloc area (i.e. below PAGE_OFFSET).

Now, according to the kernel's memory.h, converting a virtual address to
a physical address should be done like below:

	phys_addr_t __x = (phys_addr_t)(x);                             \
	__x & BIT(VA_BITS - 1) ? (__x & ~PAGE_OFFSET) + PHYS_OFFSET :   \
				 (__x - kimage_voffset); })

Please note that PHYS_OFFSET is no more equal to the start address of
the first usable memory block in SYSTEM RAM due to the fact mentioned
above.

This patch addresses this change and allows the crash utility to access
memory contents with correct addresses.

* On a live system, crash with this patch won't work, especially
  with CONFIG_RANDOMIZE_RAM configured, because we currently have no way
  to know kimage_voffset.

* For a core dump file, we can do simply:
       $ crash <vmlinux> <vmcore>
  as long as the file has "NUMBER(kimage_voffset)"
  (RELOC_AUTO|KASLR is automatically set.)

  I'm planning to add this enhancement in my next version of kexec/kdump
  patch, i.e. v17.

Signed-off-by: AKASHI Takahiro <takahiro.akashi(a)linaro.org&gt;
---
 arm64.c   | 218 ++++++++++++++++++++++++++++++++++++++++++++++++--------------
 defs.h    |  24 +++++--
 main.c    |   7 +-
 symbols.c |  12 ++--
 4 files changed, 197 insertions(+), 64 deletions(-)

diff --git a/arm64.c b/arm64.c
index 34c8c59..c16ea67 100644
--- a/arm64.c
+++ b/arm64.c
@@ -72,6 +72,21 @@ static int arm64_get_crash_notes(void);
 static void arm64_calc_VA_BITS(void);
 static int arm64_is_uvaddr(ulong, struct task_context *);
 
+ulong
+arm64_VTOP(ulong addr)
+{
+	if (!(machdep->flags & NEW_VMEMMAP) ||
+            (addr >= machdep->machspec->page_offset)) {
+		return machdep->machspec->phys_offset
+			+ (addr - machdep->machspec->page_offset);
+	} else {
+		if (machdep->machspec->kimage_voffset)
+			return addr - machdep->machspec->kimage_voffset;
+		else /* no randomness */
+			return machdep->machspec->phys_offset
+				+ (addr - machdep->machspec->vmalloc_start_addr);
+	}
+}
 
 /*
  * Do all necessary machine-specific setup here. This is called several times
@@ -81,6 +96,7 @@ void
 arm64_init(int when)
 {
 	ulong value;
+	char *string;
 	struct machine_specific *ms;
 
 #if defined(__x86_64__)
@@ -102,9 +118,33 @@ arm64_init(int when)
 		if (machdep->cmdline_args[0])
 			arm64_parse_cmdline_args();
 		machdep->flags |= MACHDEP_BT_TEXT;
+
+		ms = machdep->machspec;
+		if (!ms->kimage_voffset &&
+		    (string = pc->read_vmcoreinfo("NUMBER(kimage_voffset)"))) {
+			ms->kimage_voffset = htol(string, QUIET, NULL);
+			free(string);
+		}
+
+		if (ms->kimage_voffset) {
+			machdep->flags |= NEW_VMEMMAP;
+
+			/*
+			 * Even if CONFIG_RANDOMIZE_RAM is not configured,
+			 * derive_kaslr_offset() should work and set
+			 * kt->relocate to 0
+			 */
+			if (!kt->relocate && !(kt->flags2 & (RELOC_AUTO|KASLR)))
+				kt->flags2 |= (RELOC_AUTO|KASLR);
+		}
+
 		break;
 
 	case PRE_GDB:
+		/* This check is somewhat redundant */
+		if (kernel_symbol_exists("kimage_voffset"))
+			machdep->flags |= NEW_VMEMMAP;
+
 		if (!machdep->pagesize) {
 			/*
 			 * Kerneldoc Documentation/arm64/booting.txt describes
@@ -160,16 +200,35 @@ arm64_init(int when)
 		machdep->pagemask = ~((ulonglong)machdep->pageoffset);
 
 		arm64_calc_VA_BITS();
-		machdep->machspec->page_offset = ARM64_PAGE_OFFSET;
+		ms = machdep->machspec;
+		ms->page_offset = ARM64_PAGE_OFFSET;
+		/* FIXME: idmap for NEW_VMEMMAP */
 		machdep->identity_map_base = ARM64_PAGE_OFFSET;
-		machdep->machspec->userspace_top = ARM64_USERSPACE_TOP;
-		machdep->machspec->modules_vaddr = ARM64_MODULES_VADDR;
-		machdep->machspec->modules_end = ARM64_MODULES_END;
-		machdep->machspec->vmalloc_start_addr = ARM64_VMALLOC_START;
-		machdep->machspec->vmalloc_end = ARM64_VMALLOC_END;
-		machdep->kvbase = ARM64_VMALLOC_START;
-		machdep->machspec->vmemmap_vaddr = ARM64_VMEMMAP_VADDR;
-		machdep->machspec->vmemmap_end = ARM64_VMEMMAP_END;
+		machdep->kvbase = ARM64_VA_START;
+		ms->userspace_top = ARM64_USERSPACE_TOP;
+		if (machdep->flags & NEW_VMEMMAP) {
+			struct syment *sp;
+
+			sp = kernel_symbol_search("_text");
+			ms->kimage_text = (sp ? sp->value : 0);
+			sp = kernel_symbol_search("_end");
+			ms->kimage_end = (sp ? sp->value : 0);
+
+			ms->modules_vaddr = ARM64_VA_START;
+			if (kernel_symbol_exists("kasan_init"))
+				ms->modules_vaddr += ARM64_KASAN_SHADOW_SIZE;
+			ms->modules_end = ms->modules_vaddr
+						+ ARM64_MODULES_VSIZE -1;
+
+			ms->vmalloc_start_addr = ms->modules_end + 1;
+		} else {
+			ms->modules_vaddr = ARM64_PAGE_OFFSET - MEGABYTES(64);
+			ms->modules_end = ARM64_PAGE_OFFSET - 1;
+			ms->vmalloc_start_addr = ARM64_VA_START;
+		}
+		ms->vmalloc_end = ARM64_VMALLOC_END;
+		ms->vmemmap_vaddr = ARM64_VMEMMAP_VADDR;
+		ms->vmemmap_end = ARM64_VMEMMAP_END;
 
 		switch (machdep->pagesize)
 		{
@@ -232,8 +291,6 @@ arm64_init(int when)
 		machdep->stacksize = ARM64_STACK_SIZE;
 		machdep->flags |= VMEMMAP;
 
-		arm64_calc_phys_offset();
-		
 		machdep->uvtop = arm64_uvtop;
 		machdep->kvtop = arm64_kvtop;
 		machdep->is_kvaddr = generic_is_kvaddr;
@@ -262,6 +319,10 @@ arm64_init(int when)
 		machdep->dumpfile_init = NULL;
 		machdep->verify_line_number = NULL;
 		machdep->init_kernel_pgd = arm64_init_kernel_pgd;
+
+		/* use machdep parameters */
+		arm64_calc_phys_offset();
+
 		break;
 
 	case POST_GDB:
@@ -409,6 +470,8 @@ arm64_dump_machdep_table(ulong arg)
 		fprintf(fp, "%sIRQ_STACKS", others++ ? "|" : "");
 	if (machdep->flags & MACHDEP_BT_TEXT)
 		fprintf(fp, "%sMACHDEP_BT_TEXT", others++ ? "|" : "");
+	if (machdep->flags & NEW_VMEMMAP)
+		fprintf(fp, "%sNEW_VMEMMAP", others++ ? "|" : "");
 	fprintf(fp, ")\n");
 
 	fprintf(fp, "              kvbase: %lx\n", machdep->kvbase);
@@ -503,6 +566,11 @@ arm64_dump_machdep_table(ulong arg)
 	fprintf(fp, "           modules_end: %016lx\n", ms->modules_end);
 	fprintf(fp, "         vmemmap_vaddr: %016lx\n", ms->vmemmap_vaddr);
 	fprintf(fp, "           vmemmap_end: %016lx\n", ms->vmemmap_end);
+	if (machdep->flags & NEW_VMEMMAP) {
+		fprintf(fp, "           kimage_text: %016lx\n", ms->kimage_text);
+		fprintf(fp, "            kimage_end: %016lx\n", ms->kimage_end);
+		fprintf(fp, "        kimage_voffset: %016lx\n", ms->kimage_voffset);
+	}
 	fprintf(fp, "           phys_offset: %lx\n", ms->phys_offset);
 	fprintf(fp, "__exception_text_start: %lx\n", ms->__exception_text_start);
 	fprintf(fp, "  __exception_text_end: %lx\n", ms->__exception_text_end);
@@ -543,6 +611,42 @@ arm64_dump_machdep_table(ulong arg)
 	}
 }
 
+static int
+arm64_parse_machdep_arg_l(char *argstring, char *param, ulong *value)
+{
+	int len;
+	int megabytes = FALSE;
+	char *p;
+
+	len = strlen(param);
+	if (!STRNEQ(argstring, param) || (argstring[len] != '='))
+		return FALSE;
+
+	if ((LASTCHAR(argstring) == 'm') ||
+	    (LASTCHAR(argstring) == 'M')) {
+		LASTCHAR(argstring) = NULLCHAR;
+		megabytes = TRUE;
+	}
+
+	p = argstring + len + 1;
+	if (strlen(p)) {
+		int flags = RETURN_ON_ERROR | QUIET;
+		int err = 0;
+
+		if (megabytes) {
+			*value = dtol(p, flags, &err);
+			if (!err)
+				*value = MEGABYTES(*value);
+		} else {
+			*value = htol(p, flags, &err);
+		}
+
+		if (!err)
+			return TRUE;
+	}
+
+	return FALSE;
+}
 
 /*
  * Parse machine dependent command line arguments.
@@ -554,11 +658,10 @@ arm64_dump_machdep_table(ulong arg)
 static void
 arm64_parse_cmdline_args(void)
 {
-	int index, i, c, err;
+	int index, i, c;
 	char *arglist[MAXARGS];
 	char buf[BUFSIZE];
 	char *p;
-	ulong value = 0;
 
 	for (index = 0; index < MAX_MACHDEP_ARGS; index++) {
 		if (!machdep->cmdline_args[index])
@@ -580,39 +683,23 @@ arm64_parse_cmdline_args(void)
 		c = parse_line(buf, arglist);
 
 		for (i = 0; i < c; i++) {
-			err = 0;
-
-			if (STRNEQ(arglist[i], "phys_offset=")) {
-				int megabytes = FALSE;
-				int flags = RETURN_ON_ERROR | QUIET;
-
-				if ((LASTCHAR(arglist[i]) == 'm') ||
-				    (LASTCHAR(arglist[i]) == 'M')) {
-					LASTCHAR(arglist[i]) = NULLCHAR;
-					megabytes = TRUE;
-				}
-
-				p = arglist[i] + strlen("phys_offset=");
-				if (strlen(p)) {
-					if (megabytes)
-						value = dtol(p, flags, &err);
-					else
-						value = htol(p, flags, &err);
-				}
-
-				if (!err) {
-					if (megabytes)
-						value = MEGABYTES(value);
-
-					machdep->machspec->phys_offset = value;
-
-					error(NOTE,
-					    "setting phys_offset to: 0x%lx\n\n",
-						machdep->machspec->phys_offset);
+			if (arm64_parse_machdep_arg_l(arglist[i],
+					"phys_offset",
+					&machdep->machspec->phys_offset)) {
+				error(NOTE,
+					"setting phys_offset to: 0x%lx\n\n",
+					machdep->machspec->phys_offset);
+
+				machdep->flags |= PHYS_OFFSET;
+				continue;
+			} else if (arm64_parse_machdep_arg_l(arglist[i],
+					"kimage_voffset",
+					&machdep->machspec->kimage_voffset)) {
+				error(NOTE,
+					"setting kimage_voffset to: 0x%lx\n\n",
+					machdep->machspec->kimage_voffset);
 
-					machdep->flags |= PHYS_OFFSET;
-					continue;
-				}
+				continue;
 			}
 
 			error(WARNING, "ignoring --machdep option: %s\n",
@@ -631,6 +718,19 @@ arm64_calc_phys_offset(void)
 	if (machdep->flags & PHYS_OFFSET) /* --machdep override */
 		return;
 
+	if (machdep->flags & NEW_VMEMMAP) {
+		struct syment *sp;
+		ulong value;
+
+		sp = kernel_symbol_search("memstart_addr");
+		if (sp && readmem(sp->value, KVADDR, (char *)&value,
+				sizeof(value), "memstart_addr",
+				QUIET|RETURN_ON_ERROR)) {
+			ms->phys_offset = value;
+			return;
+		}
+	}
+
 	/*
 	 * Next determine suitable value for phys_offset. User can override this
 	 * by passing valid '--machdep phys_offset=<addr>' option.
@@ -2377,6 +2477,11 @@ arm64_IS_VMALLOC_ADDR(ulong vaddr)
 {
 	struct machine_specific *ms = machdep->machspec;
 	
+	if ((machdep->flags & NEW_VMEMMAP) &&
+	    (vaddr >= machdep->machspec->kimage_text) &&
+	    (vaddr <= machdep->machspec->kimage_end))
+		return FALSE;
+
         return ((vaddr >= ms->vmalloc_start_addr && vaddr <=
ms->vmalloc_end) ||
                 ((machdep->flags & VMEMMAP) &&
                  (vaddr >= ms->vmemmap_vaddr && vaddr <=
ms->vmemmap_end)) ||
@@ -2407,7 +2512,10 @@ arm64_calc_VA_BITS(void)
 
 	for (bitval = highest_bit_long(value); bitval; bitval--) {
 		if ((value & (1UL << bitval)) == 0) {
-			machdep->machspec->VA_BITS = bitval + 2;
+			if (machdep->flags & NEW_VMEMMAP)
+				machdep->machspec->VA_BITS = bitval + 1;
+			else
+				machdep->machspec->VA_BITS = bitval + 2;
 			break;
 		}
 	}
@@ -2459,10 +2567,22 @@ arm64_calc_virtual_memory_ranges(void)
 		break;
         }
 
-	vmemmap_size = ALIGN((1UL << (ms->VA_BITS - machdep->pageshift)) *
SIZE(page), PUD_SIZE);
+	if (machdep->flags & NEW_VMEMMAP)
+#define STRUCT_PAGE_MAX_SHIFT   6
+		vmemmap_size = 1UL << (ms->VA_BITS - machdep->pageshift - 1
+						+ STRUCT_PAGE_MAX_SHIFT);
+	else
+		vmemmap_size = ALIGN((1UL << (ms->VA_BITS - machdep->pageshift)) *
SIZE(page), PUD_SIZE);
+
 	vmalloc_end = (ms->page_offset - PUD_SIZE - vmemmap_size - SZ_64K);
-	vmemmap_start = vmalloc_end + SZ_64K;
-	vmemmap_end = vmemmap_start + vmemmap_size;
+
+	if (machdep->flags & NEW_VMEMMAP) {
+		vmemmap_start = ms->page_offset - vmemmap_size;
+		vmemmap_end = ms->page_offset;
+	} else {
+		vmemmap_start = vmalloc_end + SZ_64K;
+		vmemmap_end = vmemmap_start + vmemmap_size;
+	}
 
 	ms->vmalloc_end = vmalloc_end - 1;
 	ms->vmemmap_vaddr = vmemmap_start;
diff --git a/defs.h b/defs.h
index 7af320a..406a865 100644
--- a/defs.h
+++ b/defs.h
@@ -2846,8 +2846,8 @@ typedef u64 pte_t;
 
 #define PTOV(X) \
 	((unsigned
long)(X)-(machdep->machspec->phys_offset)+(machdep->machspec->page_offset))
-#define VTOP(X) \
-	((unsigned
long)(X)-(machdep->machspec->page_offset)+(machdep->machspec->phys_offset))
+
+#define VTOP(X)               arm64_VTOP((ulong)(X))
 
 #define USERSPACE_TOP   (machdep->machspec->userspace_top)
 #define PAGE_OFFSET     (machdep->machspec->page_offset)
@@ -2940,18 +2940,23 @@ typedef signed int s32;
 #define VM_L3_4K      (0x10)
 #define KDUMP_ENABLED (0x20)
 #define IRQ_STACKS    (0x40)
+#define NEW_VMEMMAP   (0x80)
 
 /* 
  * sources: Documentation/arm64/memory.txt 
  *          arch/arm64/include/asm/memory.h 
  *          arch/arm64/include/asm/pgtable.h
  */
-
-#define ARM64_PAGE_OFFSET    ((0xffffffffffffffffUL) <<
(machdep->machspec->VA_BITS - 1))
+#define ARM64_VA_START       ((0xffffffffffffffffUL) \
+					<< machdep->machspec->VA_BITS)
+#define ARM64_PAGE_OFFSET    ((0xffffffffffffffffUL) \
+					<< (machdep->machspec->VA_BITS - 1))
 #define ARM64_USERSPACE_TOP  ((1UL) << machdep->machspec->VA_BITS)
-#define ARM64_MODULES_VADDR  (ARM64_PAGE_OFFSET - MEGABYTES(64))
-#define ARM64_MODULES_END    (ARM64_PAGE_OFFSET - 1)
-#define ARM64_VMALLOC_START  ((0xffffffffffffffffUL) <<
machdep->machspec->VA_BITS)
+
+/* only used for v4.6 or later */
+#define ARM64_MODULES_VSIZE     MEGABYTES(128)
+#define ARM64_KASAN_SHADOW_SIZE (1UL << (machdep->machspec->VA_BITS - 3))
+
 /*
  * The following 3 definitions are the original values, but are obsolete
  * for 3.17 and later kernels because they are now build-time calculations.
@@ -3030,6 +3035,10 @@ struct machine_specific {
 	ulong kernel_flags;
 	ulong irq_stack_size;
 	ulong *irq_stacks;
+	/* only needed for v4.6 or later kernel */
+	ulong kimage_voffset;
+	ulong kimage_text;
+	ulong kimage_end;
 };
 
 struct arm64_stackframe {
@@ -5387,6 +5396,7 @@ void unwind_backtrace(struct bt_info *);
 #ifdef ARM64
 void arm64_init(int);
 void arm64_dump_machdep_table(ulong);
+ulong arm64_VTOP(ulong);
 int arm64_IS_VMALLOC_ADDR(ulong);
 ulong arm64_swp_type(ulong);
 ulong arm64_swp_offset(ulong);
diff --git a/main.c b/main.c
index 05787f0..4065e9a 100644
--- a/main.c
+++ b/main.c
@@ -227,9 +227,10 @@ main(int argc, char **argv)
 						optarg);
 				}
 			} else if (STREQ(long_options[option_index].name, "kaslr")) {
-				if (!machine_type("X86_64"))
-					error(INFO, "--kaslr only valid "
-						"with X86_64 machine type.\n");
+				if (!machine_type("X86_64") &&
+				    !machine_type("ARM64"))
+					error(INFO, "--kaslr not valid "
+						"with this machine type.\n");
 				else if (STREQ(optarg, "auto"))
 					kt->flags2 |= (RELOC_AUTO|KASLR);
 				else {
diff --git a/symbols.c b/symbols.c
index a8d3563..b0a6461 100644
--- a/symbols.c
+++ b/symbols.c
@@ -593,7 +593,8 @@ kaslr_init(void)
 {
 	char *string;
 
-	if (!machine_type("X86_64") || (kt->flags & RELOC_SET))
+	if ((!machine_type("X86_64") && !machine_type("ARM64")) ||
+	    (kt->flags & RELOC_SET))
 		return;
 
 	/*
@@ -712,7 +713,7 @@ store_symbols(bfd *abfd, int dynamic, void *minisyms, long symcount,
 	if (machine_type("X86")) {
 		if (!(kt->flags & RELOC_SET))
 			kt->flags |= RELOC_FORCE;
-	} else if (machine_type("X86_64")) {
+	} else if (machine_type("X86_64") || machine_type("ARM64")) {
 		if ((kt->flags2 & RELOC_AUTO) && !(kt->flags & RELOC_SET))
 			derive_kaslr_offset(abfd, dynamic, from,
 				fromend, size, store);
@@ -783,7 +784,8 @@ store_sysmap_symbols(void)
                 error(FATAL, "symbol table namespace malloc: %s\n",
                         strerror(errno));
 
-	if (!machine_type("X86") && !machine_type("X86_64"))
+	if (!machine_type("X86") && !machine_type("X86_64")
&&
+	    !machine_type("ARM64"))
 		kt->flags &= ~RELOC_SET;
 
 	first = 0;
@@ -833,7 +835,7 @@ store_sysmap_symbols(void)
 }
 
 /*
- *  Handle x86 kernels configured such that the vmlinux symbols
+ *  Handle x86/arm64 kernels configured such that the vmlinux symbols
  *  are not as loaded into the kernel (not unity-mapped).
  */
 static ulong
@@ -4681,7 +4683,7 @@ value_search(ulong value, ulong *offset)
 	if ((sp = machdep->value_to_symbol(value, offset)))
 		return sp;
 
-	if (IS_VMALLOC_ADDR(value)) 
+	if (IS_VMALLOC_ADDR(value))
 		goto check_modules;
 
 	if ((sp = symval_hash_search(value)) == NULL)
-- 
2.8.1


    

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[Crash-utility] [PATH v4 1/2] arm64: fix kernel memory map handling for kaslr-enabled kernel