Hi, This patch is still rough-edged, but please review it and any comments are very welcome. I will try to fix the known issues before I submit a new version of kexec/kdump patch for v4.7 merge window. Thanks, -Takahiro AKASHI ===8<=== From: AKASHI Takahiro <takahiro.akashi(a)linaro.org&gt; Date: Mon, 16 May 2016 17:31:55 +0900 Subject: [PATCH v1] arm64: fix kernel memory map handling for kaslr-enabled kernel 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. *However*, it is still rough-edged and we need more refinements. 1) Currently we have to specify the following command line: $ crash --kaslr auto --machdep phys_offset=XXX --machdep kimage_voffset=YYY <vmlinux> <vmcore> To remove these extra options, I'm planning to enhance my kdump patch so that /proc/vmcore holds the necessary information for analyzing the contents of kernel memory. 2) My current change breaks the backward compatibility. Crash won't work with v4.5 or early kernel partly because I changed the calculation of VA_BITS. (I think that the existing code is wrong.) So far I don't have enough time to look into this issue as I'm focusing on KASLR support. 3) Backtracing a 'panic'ed task fails: crash> bt PID: 999 TASK: ffffffe960081800 CPU: 0 COMMAND: "sh" bt: WARNING: corrupt prstatus? pstate=0x80000000, but no user frame found bt: WARNING: cannot determine starting stack frame for task ffffffe960081800 frame->pc indicates that it is a kernel address, so obviously something is wrong. I'm diggin into it. Signed-off-by: AKASHI Takahiro <takahiro.akashi(a)linaro.org&gt; --- arm64.c | 165 +++++++++++++++++++++++++++++++++++++++++++++----------------- defs.h | 22 ++++++--- main.c | 7 +-- symbols.c | 10 ++-- 4 files changed, 146 insertions(+), 58 deletions(-) diff --git a/arm64.c b/arm64.c index 34c8c59..22ddade 100644 --- a/arm64.c +++ b/arm64.c @@ -22,6 +22,8 @@ #include <endian.h> #define NOT_IMPLEMENTED(X) error((X), "%s: function not implemented\n", __func__) +/* FIXME: temporarily used in kt->flags2 */ +#define ARM64_NEW_VMEMMAP 0x80000000 static struct machine_specific arm64_machine_specific = { 0 }; static int arm64_verify_symbol(const char *, ulong, char); @@ -72,6 +74,21 @@ 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 (!(kt->flags2 & ARM64_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 @@ -105,6 +122,10 @@ arm64_init(int when) break; case PRE_GDB: + /* FIXME: Is kimage_voffset appropriate? */ + if (kernel_symbol_exists("kimage_voffset")) + kt->flags2 |= ARM64_NEW_VMEMMAP; + if (!machdep->pagesize) { /* * Kerneldoc Documentation/arm64/booting.txt describes @@ -160,16 +181,33 @@ 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; 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; + ms->userspace_top = ARM64_USERSPACE_TOP; + if (kt->flags2 & ARM64_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) { @@ -543,6 +581,42 @@ 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. @@ -580,39 +654,23 @@ 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", @@ -2377,6 +2435,11 @@ arm64_IS_VMALLOC_ADDR(ulong vaddr) { struct machine_specific *ms = machdep->machspec; + if ((kt->flags2 & ARM64_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 +2470,11 @@ arm64_calc_VA_BITS(void) for (bitval = highest_bit_long(value); bitval; bitval--) { if ((value & (1UL << bitval)) == 0) { +#if 1 + machdep->machspec->VA_BITS = bitval + 1; +#else /* FIXME: bug? */ machdep->machspec->VA_BITS = bitval + 2; +#endif break; } } @@ -2459,10 +2526,20 @@ arm64_calc_virtual_memory_ranges(void) break; } - vmemmap_size = ALIGN((1UL << (ms->VA_BITS - machdep->pageshift)) * SIZE(page), PUD_SIZE); + if (kt->flags2 & ARM64_NEW_VMEMMAP) { +#define STRUCT_PAGE_MAX_SHIFT 6 + vmemmap_size = 1UL << (ms->VA_BITS - machdep->pageshift - 1 + + STRUCT_PAGE_MAX_SHIFT); + + vmemmap_start = ms->page_offset - vmemmap_size; + vmemmap_end = ms->page_offset; + } else { + vmemmap_size = ALIGN((1UL << (ms->VA_BITS - machdep->pageshift)) * SIZE(page), PUD_SIZE); + + vmemmap_start = vmalloc_end + SZ_64K; + vmemmap_end = vmemmap_start + vmemmap_size; + } vmalloc_end = (ms->page_offset - PUD_SIZE - vmemmap_size - SZ_64K); - 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 a09fa9a..40e02fc 100644 --- a/defs.h +++ b/defs.h @@ -2844,8 +2844,8 @@ 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) @@ -2944,12 +2944,16 @@ typedef signed int s32; * 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. @@ -3028,6 +3032,10 @@ struct machine_specific { ulong kernel_flags; ulong irq_stack_size; ulong *irq_stacks; + /* only needed for kaslr-enabled kernel */ + ulong kimage_voffset; + ulong kimage_text; + ulong kimage_end; }; struct arm64_stackframe { diff --git a/main.c b/main.c index 821bb4e..3f24908 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..df27793 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; @@ -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