c6cfcbd8ca
The following warning is reported when frame pointers and kernel IBT are enabled: vmlinux.o: warning: objtool: ibt_selftest+0x11: sibling call from callable instruction with modified stack frame The problem is that objtool interprets the indirect branch in ibt_selftest() as a sibling call, and GCC inserts a (partial) frame pointer prologue before it: 0000 000000000003f550 <ibt_selftest>: 0000 3f550: f3 0f 1e fa endbr64 0004 3f554: e8 00 00 00 00 call 3f559 <ibt_selftest+0x9> 3f555: R_X86_64_PLT32 __fentry__-0x4 0009 3f559: 55 push %rbp 000a 3f55a: 48 8d 05 02 00 00 00 lea 0x2(%rip),%rax # 3f563 <ibt_selftest_ip> 0011 3f561: ff e0 jmp *%rax Note the inline asm is missing ASM_CALL_CONSTRAINT, so the 'push %rbp' happens before the indirect branch and the 'mov %rsp, %rbp' happens afterwards. Simplify the generated code and make it easier to understand for both tools and humans by moving the selftest to proper asm. Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/99a7e16b97bda97bf0a04aa141d6241cd8a839a2.1680912949.git.jpoimboe@kernel.org
132 lines
3.1 KiB
C
132 lines
3.1 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/ptrace.h>
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#include <asm/bugs.h>
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#include <asm/traps.h>
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enum cp_error_code {
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CP_EC = (1 << 15) - 1,
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CP_RET = 1,
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CP_IRET = 2,
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CP_ENDBR = 3,
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CP_RSTRORSSP = 4,
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CP_SETSSBSY = 5,
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CP_ENCL = 1 << 15,
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};
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static const char cp_err[][10] = {
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[0] = "unknown",
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[1] = "near ret",
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[2] = "far/iret",
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[3] = "endbranch",
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[4] = "rstorssp",
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[5] = "setssbsy",
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};
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static const char *cp_err_string(unsigned long error_code)
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{
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unsigned int cpec = error_code & CP_EC;
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if (cpec >= ARRAY_SIZE(cp_err))
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cpec = 0;
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return cp_err[cpec];
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}
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static void do_unexpected_cp(struct pt_regs *regs, unsigned long error_code)
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{
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WARN_ONCE(1, "Unexpected %s #CP, error_code: %s\n",
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user_mode(regs) ? "user mode" : "kernel mode",
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cp_err_string(error_code));
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}
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static DEFINE_RATELIMIT_STATE(cpf_rate, DEFAULT_RATELIMIT_INTERVAL,
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DEFAULT_RATELIMIT_BURST);
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static void do_user_cp_fault(struct pt_regs *regs, unsigned long error_code)
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{
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struct task_struct *tsk;
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unsigned long ssp;
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/*
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* An exception was just taken from userspace. Since interrupts are disabled
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* here, no scheduling should have messed with the registers yet and they
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* will be whatever is live in userspace. So read the SSP before enabling
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* interrupts so locking the fpregs to do it later is not required.
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*/
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rdmsrl(MSR_IA32_PL3_SSP, ssp);
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cond_local_irq_enable(regs);
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tsk = current;
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tsk->thread.error_code = error_code;
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tsk->thread.trap_nr = X86_TRAP_CP;
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/* Ratelimit to prevent log spamming. */
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if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV) &&
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__ratelimit(&cpf_rate)) {
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pr_emerg("%s[%d] control protection ip:%lx sp:%lx ssp:%lx error:%lx(%s)%s",
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tsk->comm, task_pid_nr(tsk),
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regs->ip, regs->sp, ssp, error_code,
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cp_err_string(error_code),
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error_code & CP_ENCL ? " in enclave" : "");
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print_vma_addr(KERN_CONT " in ", regs->ip);
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pr_cont("\n");
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}
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force_sig_fault(SIGSEGV, SEGV_CPERR, (void __user *)0);
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cond_local_irq_disable(regs);
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}
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static __ro_after_init bool ibt_fatal = true;
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static void do_kernel_cp_fault(struct pt_regs *regs, unsigned long error_code)
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{
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if ((error_code & CP_EC) != CP_ENDBR) {
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do_unexpected_cp(regs, error_code);
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return;
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}
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if (unlikely(regs->ip == (unsigned long)&ibt_selftest_noendbr)) {
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regs->ax = 0;
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return;
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}
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pr_err("Missing ENDBR: %pS\n", (void *)instruction_pointer(regs));
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if (!ibt_fatal) {
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printk(KERN_DEFAULT CUT_HERE);
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__warn(__FILE__, __LINE__, (void *)regs->ip, TAINT_WARN, regs, NULL);
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return;
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}
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BUG();
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}
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static int __init ibt_setup(char *str)
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{
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if (!strcmp(str, "off"))
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setup_clear_cpu_cap(X86_FEATURE_IBT);
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if (!strcmp(str, "warn"))
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ibt_fatal = false;
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return 1;
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}
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__setup("ibt=", ibt_setup);
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DEFINE_IDTENTRY_ERRORCODE(exc_control_protection)
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{
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if (user_mode(regs)) {
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if (cpu_feature_enabled(X86_FEATURE_USER_SHSTK))
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do_user_cp_fault(regs, error_code);
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else
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do_unexpected_cp(regs, error_code);
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} else {
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if (cpu_feature_enabled(X86_FEATURE_IBT))
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do_kernel_cp_fault(regs, error_code);
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else
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do_unexpected_cp(regs, error_code);
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}
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}
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