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/** @file @brief Common structures and macroses for system call hooks @details Copyright (c) 2017-2022 Acronis International GmbH @author Mikhail Molchanov (Mikhail.Molchanov@acronis.com) @since $Id: $ */ #pragma once #include "module_rundown_protection.h" #include "stringify.h" #include "syscall_utils.h" #include <linux/types.h> // bool /* * ============================================================================ * * Here is the short summary about different types of compatibility syscalls ( * based mostly on lwn.net "Anatomy of a system call, part 1" and "..., part 2": * https://lwn.net/Articles/604287/ and https://lwn.net/Articles/604515/, * respectively): * * ---------------------------------------------------------------------------- * * First, you need to know that there are userspace and kernelspace components * each of which could either have 32 or 64-bit bitness: * * 1) 32-bit kernel supports only 32-bit userspace programs. * 2) 64-bit kernel supports: * 2.a) 64-bit userspace programs (x86_64) * 2.b) 32-bit userspace programs (x86_32) * 2.c) x32 ABI userspace programs (as described on Wikipedia and "The x32 * system call ABI" lwn.net's article (https://en.wikipedia.org/wiki/X32_ABI * and https://lwn.net/Articles/456731/, respectively): * x32 ABI allows programs to take advantage of the benefits of x86_64 * instruction set (larger number of CPU registers, function parameters * passed via registers, ...) while using 32-bit pointers and thus avoiding * the overhead of 64-bit pointers (mostly expanded memory use and a larger * cache footprint)) * * ---------------------------------------------------------------------------- * * Next, take a look at "arch/x86/syscalls/syscall_32.tbl" and * "arch/x86/syscalls/syscall_64.tbl" - these are files (from which syscalls * tables are generated during the compilation of the Linux kernel) that contain * the lists of every syscall in the OS, their respective numbers, names of * functions implementing them for different bitnesses of user/kernel spaces and * some more. * * -- File "syscall_32.tbl" is present on both 32-bit and 64-bit kernel and has * the format: * <number> <abi> <name> <entry point> <compat entry point> * * Where: * <number> - system-wide unique syscall number (each has a handy * define, e.g. 'pwritev' has a number 334 and a symbolic * define for this number: '__NR_sys_pwritev') * * <name> - the actual name of the syscall (e.g. 'pwritev') * * <entry point> - the name for a function implementing given syscall for * the (1) case (as described before: 32-bit userspace * program running on 32-bit kernel); * NOTE: search implementation as * "SYSCALL_DEFINE.*(pwritev" * * <compat entry point> - the name for a function implementing given syscall for * the (2.b) case (32-bit user on 64-bit kernel); * NOTE: search implementation as * "COMPAT_SYSCALL_DEFINE.*(pwritev" * * -- File "syscall_64.tbl" is present only on 64-bit kernel and has the format: * <number> <abi> <name> <entry point> * * Where everything is similar, but: * <number> - from 0 to 511 - only (2.a) syscalls (64-bit user on 64-bit kernel) * similar to <entry point> column of * "syscall_32.tbl" * - from 512 - only (2.c) syscalls (x32 ABI) * similar to <compat entry point> column of * "syscall_32.tbl" * * ---------------------------------------------------------------------------- * * Let's examine, for example, 'pwritev()' syscall: * * -- "syscall_32.tbl" has following string for it: * <number> <abi> <name> <entry point> <compat entry point> * 334 i386 pwritev sys_pwritev compat_sys_pwritev * * -- "syscall_64.tbl" instead has two of them: * <number> <abi> <name> <entry point> * 296 64 pwritev sys_pwritev * ... * 535 x32 pwritev compat_sys_pwritev64 * * 2.a) For the most popular nowadays case (64-bit user, 64-bit kernel) all is * simple: "syscall_64.tbl" on 64-bit kernel has analogous 'sys_call_table' * in memory, so to call (2.a) 'pwritev' you need to call 'sys_pwritev' * from "syscall_64.tbl" or 'sys_call_table[__NR_pwritev]'. * NOTE: include <linux/unistd.h> for macros. * * 1) Surprisingly, for this case (32-bit user, 32-bit kernel) all is almost * the same as in the previous case: "syscall_32.tbl" on 32-bit kernel has * analogous 'sys_call_table' in memory, so to call (1) 'pwritev' you need * to call 'sys_pwritev' from "syscall_32.tbl" or 'sys_call_table[__NR_pwritev]'. * * Now for mixed bitnesses: * 2.b) There (32-bit user, 64-bit kernel) you need 'compat_sys_pwritev' from * "syscall_32.tbl", but remember - you have 64-bit kernel, so "syscall_32.tbl" * won't be called 'sys_call_table' in memory (as it's the in-memory name * for the 64-bit syscalls table) but rather 'ia32_sys_call_table' and the * number of 'pwritev' from this "syscall_32.tbl" might be different from * the number of ordinary (2.a) 'pwritev' from "syscall_64.tbl", so to call * (2.b) 'pwritev' you need to call 'compat_sys_pwritev' from "syscall_32.tbl" * or 'ia32_sys_call_table[__NR_ia32_pwritev]'. * NOTE: include <asm/ia32_unistd.h> for macros. * * 2.c) Lastly, (x32 ABI) you need 'compat_sys_pwritev64' from "syscall_64.tbl"; * as before, "syscall_64.tbl" has analogous 'sys_call_table' in memory but * 'pwritev' is x32 ABI now, so it'll have its own number in this table * (different from ordinary (2.a) 'pwrite'), because of that, to call * (2.c) 'pwritev' do 'sys_call_table[__NR_x32_pwritev]'. * * * Once again (now with some ASCII art; here 32u = 32-bit userspace, * 64k = 64-bit kernelspace and so on): * -- "syscall_32.tbl": * <number> <abi> <name> <entry point> <compat entry point> * 334 i386 pwritev sys_pwritev compat_sys_pwritev * ^ ^ * | | * ((1): 32u on 32k) ((2.b): 32u on 64k) * * -- "syscall_64.tbl": * <number> <abi> <name> <entry point> * 296 64 pwritev sys_pwritev <---------- ((2.a): 64u on 64k) * ... * 535 x32 pwritev compat_sys_pwritev64 <-- ((2.c): x32 ABI) * * ---------------------------------------------------------------------------- * * And the last thing: * if in "syscall_32.tbl" or "syscall_64.tbl" there is a blank cell in the table * instead of a compat syscall name ((2.b): 32u on 64k or (2.c): x32 ABI, * respectively) this means that there is no need for dedicated compat syscall * and ordinary syscall ((1): 32u on 32k or (2.a): 64u on 64k) is doing both * jobs: its and compat's one. So, to call, for example (2.b): 32u on 64k 'creat', * as with ordinary (2.b) do 'ia32_sys_call_table[__NR_ia32_creat]' and this * will call 'sys_creat' that is doing its and imaginary 'compat_sys_creat's job. * * There are even syscalls (e.g. ordinary 'read' or 'write') that have single * implementation for all four cases: (1): 32u on 32k, (2.a): 64u on 64k, * (2.b): 32u on 64k and (2.c): x32 ABI, and there is nothing strange, because * we need distinct compat functions only if syscall needs to "cope with * pointer-to-pointer arguments or pointer-to-struct-containing-pointer * arguments, for example 'struct iovec'". * * ============================================================================ */ #ifdef __NR_renameat2 #define RENAMEAT2_ENABLED true #else #define __NR_renameat2 316 #define RENAMEAT2_ENABLED false #endif #ifdef __NR_preadv2 #define PREADV2_ENABLED true #else #define __NR_preadv2 327 #define PREADV2_ENABLED false #endif #ifdef __NR_pwritev2 #define PWRITEV2_ENABLED true #else #define __NR_pwritev2 328 #define PWRITEV2_ENABLED false #endif /* * This is for both (1) and (2.a) cases, depending on the bitness of the kernel. */ #define DEFINE_HOOK_DESC(abi, tag, enabled) \ { \ NULL, \ SYSCALL_HOOK_TRAMPOLINE(abi, tag), \ STRINGIFY(SYSCALL_HOOK_TRAMPOLINE(abi, tag)), \ __NR_##tag, \ enabled \ } #define SYSCALL_ORIG(abi, tag) \ ( \ (SYSCALL_ORIG_TYPE_NAME(abi, tag)) \ (hook_table[SYSCALL_HOOK_ID(abi, tag)].syscall_orig) \ ) #define SYSCALL_ORIG_FN(abi, tag) \ ( \ (long) (hook_table[SYSCALL_HOOK_ID(abi, tag)].syscall_orig) \ ) /* * This is for (2.b) case, but when <compat entry point> cell is empty in "syscall_32.tbl". * This means that hook has the same prototype as (2.a) but needs to be called using * 'ia32_sys_call_table' just like (2.b). */ #define DEFINE_IA32_HOOK_DESC(abi, tag, enabled) \ { \ NULL, \ SYSCALL_HOOK_TRAMPOLINE(abi, tag), \ STRINGIFY(SYSCALL_HOOK_TRAMPOLINE(abi, tag)), \ __NR_ia32_##tag, \ enabled \ } #define IA32_SYSCALL_ORIG(abi, tag) \ ( \ (SYSCALL_ORIG_TYPE_NAME(abi, tag)) \ (ia32_hook_table[SYSCALL_HOOK_ID(abi, tag)].syscall_orig) \ ) #define IA32_SYSCALL_ORIG_FN(abi, tag) \ ( \ (long) (ia32_hook_table[SYSCALL_HOOK_ID(abi, tag)].syscall_orig) \ ) /* * This is for (2.b) case. */ #define DEFINE_COMPAT_HOOK_DESC(abi, tag, enabled) \ { \ NULL, \ SYSCALL_HOOK_TRAMPOLINE(abi, tag), \ STRINGIFY(SYSCALL_HOOK_TRAMPOLINE(abi, tag)), \ __NR_ia32_##tag, \ enabled \ } #define DEFINE_COMPAT_HOOK_DESC_PRE(abi, tag, enabled) \ { \ NULL, \ SYSCALL_HOOK_NAME_PRE(abi, tag), \ STRINGIFY(SYSCALL_HOOK_NAME(abi, tag)), \ __NR_ia32_##tag, \ enabled \ } #define COMPAT_SYSCALL_ORIG(abi, tag) \ ( \ (SYSCALL_ORIG_TYPE_NAME(abi, tag)) \ (ia32_hook_table[COMPAT_SYSCALL_HOOK_ID(abi, tag)].syscall_orig) \ ) #define COMPAT_SYSCALL_ORIG_FN(abi, tag) \ ( \ (long) (ia32_hook_table[COMPAT_SYSCALL_HOOK_ID(abi, tag)].syscall_orig) \ ) enum hook_numbs { SYSCALL_HOOK_ID(sys, creat), SYSCALL_HOOK_ID(sys, open), SYSCALL_HOOK_ID(sys, openat), SYSCALL_HOOK_ID(sys, close), SYSCALL_HOOK_ID(sys, read), SYSCALL_HOOK_ID(sys, pread64), SYSCALL_HOOK_ID(sys, readv), SYSCALL_HOOK_ID(sys, preadv), SYSCALL_HOOK_ID(sys, preadv2), SYSCALL_HOOK_ID(sys, write), SYSCALL_HOOK_ID(sys, pwrite64), SYSCALL_HOOK_ID(sys, writev), SYSCALL_HOOK_ID(sys, pwritev), SYSCALL_HOOK_ID(sys, pwritev2), SYSCALL_HOOK_ID(sys, rename), SYSCALL_HOOK_ID(sys, renameat), SYSCALL_HOOK_ID(sys, renameat2), SYSCALL_HOOK_ID(sys, unlink), SYSCALL_HOOK_ID(sys, unlinkat), TOTAL_HOOKS_COUNT }; /* * There are practically no '__NR_ia32_*' macros on CentOS 6 (besides the ones * defined in "/usr/src/kernels/`uname -r`/arch/x86/include/asm/ia32_unistd.h"), * so define needed syscall numbers manually. * * Syscalls are never renumbered (on sane kernels), so get the right numbers from: * "/usr/src/kernels/`uname -r`/arch/x86/include/asm/unistd_32.h" */ #ifndef __NR_ia32_creat #define __NR_ia32_creat 8 #endif #ifndef __NR_ia32_open #define __NR_ia32_open 5 #endif #ifndef __NR_ia32_close #define __NR_ia32_close 6 #endif #ifndef __NR_ia32_openat #define __NR_ia32_openat 295 #endif #ifndef __NR_ia32_readv #define __NR_ia32_readv 145 #endif #ifndef __NR_ia32_read #define __NR_ia32_read 3 #endif #ifndef __NR_ia32_pread64 #define __NR_ia32_pread64 180 #endif #ifndef __NR_ia32_preadv #define __NR_ia32_preadv 333 #endif #ifndef __NR_ia32_preadv2 #define __NR_ia32_preadv2 378 #endif #ifndef __NR_ia32_writev #define __NR_ia32_writev 146 #endif #ifndef __NR_ia32_pwrite64 #define __NR_ia32_pwrite64 181 #endif #ifndef __NR_ia32_pwritev #define __NR_ia32_pwritev 334 #endif #ifndef __NR_ia32_rename #define __NR_ia32_rename 38 #endif #ifndef __NR_ia32_renameat #define __NR_ia32_renameat 302 #endif #ifndef __NR_ia32_unlink #define __NR_ia32_unlink 10 #endif #ifndef __NR_ia32_unlinkat #define __NR_ia32_unlinkat 301 #endif #ifndef __NR_ia32_renameat2 #define __NR_ia32_renameat2 353 #endif #ifndef __NR_ia32_pwritev2 #define __NR_ia32_pwritev2 379 #endif enum ia32_hook_numbs { SYSCALL_HOOK_ID(ia32_sys, creat), /* * In fact, it is 'compat_sys_open()', but function prototype is identical * to ordinary 'sys_open()', so to simplify our code we treat it as * 'ia32_sys_open()'. */ SYSCALL_HOOK_ID(ia32_sys, open), SYSCALL_HOOK_ID(ia32_sys, openat), SYSCALL_HOOK_ID(ia32_sys, close), SYSCALL_HOOK_ID(ia32_sys, read), COMPAT_SYSCALL_HOOK_ID(compat_sys, pread64), COMPAT_SYSCALL_HOOK_ID(compat_sys, readv), COMPAT_SYSCALL_HOOK_ID(compat_sys, preadv), COMPAT_SYSCALL_HOOK_ID(compat_sys, preadv2), SYSCALL_HOOK_ID(ia32_sys, write), COMPAT_SYSCALL_HOOK_ID(compat_sys, pwrite64), COMPAT_SYSCALL_HOOK_ID(compat_sys, writev), COMPAT_SYSCALL_HOOK_ID(compat_sys, pwritev), COMPAT_SYSCALL_HOOK_ID(compat_sys, pwritev2), SYSCALL_HOOK_ID(ia32_sys, rename), SYSCALL_HOOK_ID(ia32_sys, renameat), SYSCALL_HOOK_ID(ia32_sys, renameat2), SYSCALL_HOOK_ID(ia32_sys, unlink), SYSCALL_HOOK_ID(ia32_sys, unlinkat), TOTAL_IA32_HOOKS_COUNT }; struct hook_desc { void *syscall_orig; void *syscall_hook; const char *syscall_name; int syscall_nr; /* * If a syscall is present on the system (it depends on kernel version * <=> distro name/version) you need to set bit corresponding to this * distro in 'activation_bitmask' using appropriate macro, thus enabling * this syscall to be inserted upon driver start on this distro. */ // TODO: This is culprit, refactoring of 'fs_syscall_hooks' is required to remove it bool enabled; }; extern struct hook_desc hook_table[]; extern struct hook_desc ia32_hook_table[]; int syscall_hooks_init(void); void syscall_hooks_exit(void); int syscall_hooks_attach(void); int syscall_hooks_detach(void); #define HOOK_PROLOG() mod_rundown_protection_lock() #define HOOK_EPILOG() mod_rundown_protection_unlock()

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