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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH 1/1] kdd.c: Add support for initial handshake in KD protocol for Win 7, 8 and 10 (64 bit)
On Wed, 6 Nov 2019 at 02:24, Julian Tuminaro <julian.tuminaro@xxxxxxxxx> wrote:
>
> From: "julian.tuminaro@xxxxxxxxx" <julian.tuminaro@xxxxxxxxx>
>
>
> Current implementation of find_os is based on the hard-coded values for
> different Windows version. It uses the value for get the address to
> start looking for DOS header in the given specified range. However, this
> is not scalable to all version of Windows as it will require us to keep
> adding new entries and also due to KASLR, chances of not hitting the PE
> header is significant. We implement a way for 64-bit systems to use IDT
> entry to get a valid exception/interrupt handler and then move back into
> the memory to find the valid DOS header. Since IDT entries are protected
> by PatchGuard, we think our assumption that IDT entries will not be
> corrupted is valid for our purpose. Once we have the image base, we
> search for the DBGKD_GET_VERSION64 structure type in .data section to
> get information required for handshake.
>
> Currently, this is a work in progress feature and current patch only
> supports the handshake and memory read/write on 64-bit systems.
>
> Signed-off-by: Jenish Rakholiya <rjenish@xxxxxxx>
> Signed-off-by: Julian Tuminaro <jtuminar@xxxxxxxxxxxxxx>
Julian,
Thanks for the patch. This work is great progress for kdd. Comments
below... Mainly style-related but I think there's also some clean-up
needed and a few tweaks.
> ---
> tools/debugger/kdd/kdd.c | 389 ++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 388 insertions(+), 1 deletion(-)
>
> diff --git a/tools/debugger/kdd/kdd.c b/tools/debugger/kdd/kdd.c
> index fb8c645355..407b70a21c 100644
> --- a/tools/debugger/kdd/kdd.c
> +++ b/tools/debugger/kdd/kdd.c
> @@ -51,6 +51,8 @@
>
> #include "kdd.h"
>
> +// TODO: make fix this to actually use address instead of offset?
> +// TODO: Maybe clean something as well?
These TODOs are a not really well enough described to be committed
IMO. I'm totally fine with having TODO or FIXME comments, but they
ought to be clear enough for someone else picking up the code.
> /* Windows version details */
> typedef struct {
> uint32_t build;
> @@ -62,6 +64,7 @@ typedef struct {
> uint32_t version; /* +-> NtBuildNumber */
> uint32_t modules; /* +-> PsLoadedModuleList */
> uint32_t prcbs; /* +-> KiProcessorBlock */
> + uint32_t kddl;
Comment for this field perhaps?
> } kdd_os;
>
> /* State of the debugger stub */
> @@ -85,6 +88,106 @@ typedef struct {
> kdd_os os; /* OS-specific magic numbers
> */
> } kdd_state;
>
> +/**
> + * @brief Size of pointer on 64 machine
> + */
> +#define SIZE_PTR64 8
> +
> +/**
> + * @brief Size of pointer on 32 machine
> + */
> +#define SIZE_PTR32 4
> +
> +
> +/*****************************************************************************
> + * PE and DOS Header related offsets
> + */
> +
> +/**
> + * @brief Offset in DOS header to look for PE header
> + */
> +#define DOS_HDR_PE_OFF 0x3c
> +
> +/**
> + * @brief Size of PE header offset field in DOS header
> + */
> +#define DOS_HDR_PE_SZ 4
> +
> +/**
> + * @brief Offset of number of sections field in PE header
> + */
> +#define PE_NUM_SECTION_OFF 0x6
> +
> +/**
> + * @brief Size of number of sections field in PE header
> + */
> +#define PE_NUM_SECTION_SZ 2
> +
> +/**
> + * @brief Offset of optional header size field in PE header
> + */
> +#define PE_OPT_HDR_SZ_OFF 0x14
> +
> +/**
> + * @brief Size of optional header size field in PE header
> + */
> +#define PE_OPT_HDR_SZ_SZ 2
> +
> +/**
> + * @brief Size of PE header
> + */
> +#define PE_HDR_SZ 0x18
> +
> +/**
> + * @brief Size of section header entries in PE
> + */
> +#define PE_SECT_ENT_SZ 0x28
> +
> +/**
> + * @brief Offset of name field in section header entry
> + */
> +#define PE_SECT_NAME_OFF 0
> +
> +/**
> + * @brief Size of name field in section header entry
> + */
> +#define PE_SECT_NAME_SZ 0x8
> +
> +/**
> + * @brief Offset of virtual address (RVA) field in section header entry
> + */
> +#define PE_SECT_RVA_OFF 0xc
> +
> +/**
> + * @brief Offset of virtual size field in section header entry
> + */
> +#define PE_SECT_VSIZE_OFF 0x8
> +
> +/**
> + * @brief Size of DBGKD_GET_VERSION64 struct
> + */
> +#define DBGKD_GET_VERSION64_SZ 0x28
> +
> +/**
> + * @brief Offset of KERN_BASE in DBGKD_GET_VERSION64 struct
> + */
> +#define DBGKD_KERN_BASE_OFF 0x10
> +
> +/**
> + * @brief Offset of PsLoadedModulesList in DBGKD_GET_VERSION64 struct
> + */
> +#define DBGKD_MOD_LIST_OFF 0x18
> +
> +/**
> + * @brief Offset of DebuggerDataList in DBGKD_GET_VERSION64 struct
> + */
> +#define DBGKD_KDDL_OFF 0x20
> +
> +/**
> + * @brief Offset of DebuggerDataList in DBGKD_GET_VERSION64 struct
> + */
> +#define DBGKD_MINOR_OFF 0x2
> +
>
> /*****************************************************************************
> * Utility functions
> */
> @@ -390,6 +493,284 @@ static void find_os(kdd_state *s)
> s->os = unknown_os;
> }
>
> +#if 0
> +/**
> + * @brief Temporary function for printing memory dump while debugging
> + * Dumps in the format of QWORD type
> + *
> + * @param s Pointer to the kdd_state structure
> + * @param addr Address to start dumping memory from
> + * @param size Number of bytes to print (automatically aligned to higher
> + * multiple of 8 bytes
> + *
> + * @note TODO: Remove this before pushing to master
I guess this means you want to leave this out of the actual commit for now?
> + * @note TODO: Maybe add level of logging to kdd (using -v option) - The
> + * idea of using printf instead of KDD_LOG was to not print all other
> unwanted
> + * logging output
> + */
> +static void my_memdump(kdd_state *s, uint64_t addr, int size)
> +{
> + int ret;
> + uint64_t buf;
> +
> + // we don't handle mis-aligned addresses
General style is not to use // comments, but stick to /* */.
> + if (addr & 7) {
> + // XXX: TODO: don't do this
> + return;
> + }
No requirement for braces around single line clauses.
> +
> + // dump memory 1 QWORD at a time
> + // format: <address> [offset from start]: dump1 dump2
> + for (int i = 0; i < size; i += 16) {
> +
> + // read 8 bytes - on failure, break
> + ret = kdd_read_virtual(s, s->cpuid, addr + i, 8, &buf);
> + if (ret != 8) {
> + break;
> + }
> +
> + // print first part
> + printf("0x%p [+0x%03x]: %p ", (void *)(addr + i), i, (void *)buf);
> +
> + // read next 8 bytes and print it
> + ret = kdd_read_virtual(s, s->cpuid, addr + i + 8, 8, &buf);
> + if (ret != 8) {
> + break;
> + }
> + printf("%p\n", (void *)buf);
> + }
> + printf("\n");
> +}
> +#endif
> +
> +/**
> + * @brief Parse the memory at \a filebase as a valid DOS header and get
> virtual
> + * address offset and size for any given section name (if it exists)
> + *
> + * @param s Pointer to the kdd_state structure
> + * @param filebase Base address of the file structure
> + * @param sectname Pointer to the section name c-string to look for
> + * @param vaddr Pointer to write the virtual address of section start to
> + * (if found)
> + * @param visze Pointer to write the section size to (if found)
> + *
> + * @return -1 on failure to find the section name
> + * @return 0 on success
> + */
> +static int get_pe64_sections(kdd_state *s, uint64_t filebase, char *sectname,
> + uint64_t *vaddr, uint32_t *vsize)
> +{
> + uint8_t buf[0x30];
> + uint64_t pe_hdr;
> + uint64_t sect_start;
> + uint16_t num_sections;
> + int ret;
> +
> + ret = -1;
You could assign during declaration.
> +
> + if (!s->os.w64) {
> + return ret;
return -1, for consistency, perhaps?
> + }
> +
> + // read PE header offset
> + if (kdd_read_virtual(s, s->cpuid, filebase + DOS_HDR_PE_OFF,
> DOS_HDR_PE_SZ,
> + buf) != DOS_HDR_PE_SZ) {
> + return -1;
> + }
> +
> + pe_hdr = filebase + *(uint32_t *)buf;
> +
> + // read number of sections
> + if (kdd_read_virtual(s, s->cpuid, pe_hdr + PE_NUM_SECTION_OFF,
> + PE_NUM_SECTION_SZ, &buf) != PE_NUM_SECTION_SZ) {
> + return -1;
> + }
> + num_sections = *(uint16_t *)buf;
> +
> + // read size of optional header
> + if (kdd_read_virtual(s, s->cpuid, pe_hdr + PE_OPT_HDR_SZ_OFF,
> + PE_OPT_HDR_SZ_SZ, &buf) != PE_OPT_HDR_SZ_SZ) {
> + return -1;
> + }
> +
> + // 0x18 is the size of PE header
> + sect_start = pe_hdr + PE_HDR_SZ + *(uint16_t *)buf;
> +
> + for (int i = 0; i < num_sections; i++) {
> + if (kdd_read_virtual(s, s->cpuid, sect_start + (i * PE_SECT_ENT_SZ),
> + PE_SECT_ENT_SZ, &buf) != PE_SECT_ENT_SZ) {
> + return -1;
> + }
> +
> + if (!strncmp(sectname, (char *)(buf + PE_SECT_NAME_OFF),
> + PE_SECT_NAME_SZ)) {
> + *vaddr = filebase + *(uint32_t *)(buf + PE_SECT_RVA_OFF);
> + *vsize = *(uint32_t *)(buf + PE_SECT_VSIZE_OFF);
> + ret = 0;
> + break;
> + }
> + }
> +
> + return ret;
> +}
> +
> +/**
> + * @brief Get the OS information like base address, minor version,
> + * PsLoadedModuleList and DebuggerDataList (basically the fields of
> + * DBGKD_GET_VERSION64 struture required to do handshake?).
> + *
> + * This is done by reading the IDT entry for divide-by-zero exception and
> + * searching back into the memory for DOS header (which is our kernel base).
> + * Once we have the kernel base, we parse the PE header and look for kernel
> + * base address in the .data section. Once we have possible values, we look
> for
> + * DBGKD_GET_VERSION64 block by using following heuristics on the address
> which
> + * has the kernel base:
> + *
> + * - at address [-0x10], it should have 0xf as the MajorVersion
> + * - at address [+0x8], it should have a valid kernel memory address
> pointing
> + * in .data
> + * - at address [+0x10], it should have a valid kernel memory address
> pointing
> + * in .data
> + *
> + * @param s Pointer to the kdd state
> + */
> +static void get_os_info_64(kdd_state *s)
> +{
> + kdd_ctrl ctrl;
> + int ret;
> + uint64_t buf;
> + uint64_t idt0_addr;
> + uint64_t base;
> + uint64_t caddr;
> + uint64_t data_base;
> + uint32_t data_size;
> + uint64_t modptr;
> + uint64_t kddl;
> + uint16_t minor;
> + uint8_t dbgkd_get_version64[0x28];
> +
> + /* TODO: right now, we are forcing this to 1 (as we only support 64 bit
> + * system, however, we should use kdd_state or hvm calls to check if we
> are
> + * in 64-bit
> + */
> + s->os.w64 = 1;
> +
> + // if we are no in 64-bit mode, fail
> + if (!s->os.w64) {
> + goto fail;
> + }
> +
> + // get control registers for our os
> + ret = kdd_get_ctrl(s->guest, s->cpuid, &ctrl, s->os.w64);
> + if (ret) {
> + goto fail;
> + }
> +
> + // read the div-by-zero handler function address
> + kdd_read_virtual(s, s->cpuid, ctrl.c64.idt_base + 8, 8, &buf);
> + idt0_addr = ((uint64_t)buf << 32) & 0xffffffff00000000;
> +
> + kdd_read_virtual(s, s->cpuid, ctrl.c64.idt_base, 8, &buf);
> + idt0_addr |= ((buf >> 32) & 0xffff0000);
> + idt0_addr |= (buf & 0xffff);
> +
> + KDD_LOG(s, "idt0 addr: %p\n", (void *)idt0_addr);
> + printf("idt0 addr: %p\n", (void *)idt0_addr);
> +
> + // get the page start and look for "MZ" file header
> +
> + base = idt0_addr & ~(PAGE_SIZE - 1);
> + // printf("%p\n", (void *)base);
> +
> + while (1) {
> + uint16_t val;
> + if (kdd_read_virtual(s, s->cpuid, base, 2, &val) != 2) {
> + // just move going back?? this is bad though
> + printf("ran into unmapped region without finding PE header\n");
Bail out of the loop here, or continue? Checking val after a failure
doesn't seem right.
> + }
> +
> + if (val == 0x5a4d) { // MZ
Perhaps #define this value.
> + // printf("maybe success\n");
> + break;
> + }
> +
> + base -= PAGE_SIZE;
> + }
> +
> + KDD_LOG(s, "base: %p\n", (void *)base);
> +
> + // found the data section start
> + if (get_pe64_sections(s, base, ".data", &data_base, &data_size)) {
> + goto fail;
> + }
> +
> + // look for addresses which has kernel base written into it
> + caddr = data_base;
> +
> + modptr = 0;
> + kddl = 0;
> + minor = 0;
> +
> + while (caddr < data_base + data_size) {
> + if (kdd_read_virtual(s, s->cpuid, caddr, SIZE_PTR64, &buf) !=
> + SIZE_PTR64) {
> + // reached end and found nothing
> + goto fail;
> + }
> +
> + // if we found base in the memory addresses
> + if (buf == base) {
> + // read the DBGKD_GET_VERSION64 struct
> + if (kdd_read_virtual(s, s->cpuid, caddr - DBGKD_KERN_BASE_OFF,
> + DBGKD_GET_VERSION64_SZ, dbgkd_get_version64) ==
> + DBGKD_GET_VERSION64_SZ) {
> + // check if major version is 0xf
> + if (dbgkd_get_version64[0] == '\x0f') {
> +
> + // read minor version, PsLoadedModuleList pointer and
> + // DebuggerDataList
> + modptr =
> + *(uint64_t *)(dbgkd_get_version64 +
> DBGKD_MOD_LIST_OFF);
> + kddl = *(uint64_t *)(dbgkd_get_version64 +
> DBGKD_KDDL_OFF);
> + minor =
> + *(uint16_t *)(dbgkd_get_version64 + DBGKD_MINOR_OFF);
> +
> + // do heuristic check
> + if (modptr && kddl && modptr != kddl && kddl != base &&
> + base != modptr && modptr >= data_base &&
> + modptr < (data_base + data_size) &&
> + kddl >= data_base &&
> + kddl < (data_base + data_size)) {
> + // my_memdump(s, caddr - 0x10, 0x30);
> + break;
> + }
> +
> + }
> + }
> +
> + }
> +
> + caddr += sizeof(void *);
> + }
> +
> + // TODO: use KDD_LOG?
Looks like this should be fixed.
> + printf("base: %p\n", (void *)base);
> + printf("modules list: %p\n", (void *)modptr);
> + printf("kddl: %p\n", (void *)kddl);
> + printf("minor version: 0x%hx\n", minor);
> +
> + s->os.base = base;
> + s->os.modules = modptr - base;
> + s->os.kddl = kddl - base;
> + s->os.build = (uint32_t) minor;
> + return;
> +
> +fail:
> + // XXX: TODO: handle failure case
handle in what way?
> + s->os = unknown_os;
No need for a return here.
> + return;
> +}
> +
>
>
> /*****************************************************************************
> * How to send packets and acks.
> @@ -534,6 +915,12 @@ static void kdd_handle_handshake(kdd_state *s)
> {
> /* Figure out what we're looking at */
> find_os(s);
> +
> + /* if unknown os, use the idt method */
> + if (!s->os.base) {
> + get_os_info_64(s);
> + }
> +
> kdd_send_string(s, "[kdd: %s @0x%"PRIx64"]\r\n", s->os.name, s->os.base);
>
> /* Respond with some details about the debugger stub we simulate */
> @@ -555,7 +942,7 @@ static void kdd_handle_handshake(kdd_state *s)
> s->txp.cmd.shake.u3[2] = 0x55;
> s->txp.cmd.shake.kern_addr = s->os.base;
> s->txp.cmd.shake.mods_addr = s->os.base + s->os.modules;
> - s->txp.cmd.shake.data_addr = 0; /* Debugger data probably doesn't exist
> */
> + s->txp.cmd.shake.data_addr = s->os.base + s->os.kddl; // 0; /* Debugger
> data probably doesn't exist */
That comment doesn't sound right any more.
Thanks,
Paul
>
> KDD_LOG(s, "Client initial handshake: %s\n", s->os.name);
> kdd_send_cmd(s, KDD_CMD_SHAKE, 0);
> --
> 2.17.1
>
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