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x86/traps: Attempt to fixup exceptions in vDSO before signaling
vDSO functions can now leverage an exception fixup mechanism similar to kernel exception fixup. For vDSO exception fixup, the initial user is Intel's Software Guard Extensions (SGX), which will wrap the low-level transitions to/from the enclave, i.e. EENTER and ERESUME instructions, in a vDSO function and leverage fixup to intercept exceptions that would otherwise generate a signal. This allows the vDSO wrapper to return the fault information directly to its caller, obviating the need for SGX applications and libraries to juggle signal handlers. Attempt to fixup vDSO exceptions immediately prior to populating and sending signal information. Except for the delivery mechanism, an exception in a vDSO function should be treated like any other exception in userspace, e.g. any fault that is successfully handled by the kernel should not be directly visible to userspace. Although it's debatable whether or not all exceptions are of interest to enclaves, defer to the vDSO fixup to decide whether to do fixup or generate a signal. Future users of vDSO fixup, if there ever are any, will undoubtedly have different requirements than SGX enclaves, e.g. the fixup vs. signal logic can be made function specific if/when necessary. Suggested-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org> Signed-off-by: Borislav Petkov <bp@suse.de> Acked-by: Jethro Beekman <jethro@fortanix.com> Link: https://lkml.kernel.org/r/20201112220135.165028-19-jarkko@kernel.org
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2 changed files with 17 additions and 0 deletions
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@ -60,6 +60,7 @@
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#include <asm/umip.h>
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#include <asm/insn.h>
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#include <asm/insn-eval.h>
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#include <asm/vdso.h>
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#ifdef CONFIG_X86_64
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#include <asm/x86_init.h>
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@ -117,6 +118,9 @@ do_trap_no_signal(struct task_struct *tsk, int trapnr, const char *str,
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tsk->thread.error_code = error_code;
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tsk->thread.trap_nr = trapnr;
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die(str, regs, error_code);
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} else {
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if (fixup_vdso_exception(regs, trapnr, error_code, 0))
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return 0;
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}
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/*
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@ -550,6 +554,9 @@ DEFINE_IDTENTRY_ERRORCODE(exc_general_protection)
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tsk->thread.error_code = error_code;
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tsk->thread.trap_nr = X86_TRAP_GP;
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if (fixup_vdso_exception(regs, X86_TRAP_GP, error_code, 0))
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return;
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show_signal(tsk, SIGSEGV, "", desc, regs, error_code);
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force_sig(SIGSEGV);
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goto exit;
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@ -1048,6 +1055,9 @@ static void math_error(struct pt_regs *regs, int trapnr)
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if (!si_code)
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goto exit;
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if (fixup_vdso_exception(regs, trapnr, 0, 0))
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return;
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force_sig_fault(SIGFPE, si_code,
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(void __user *)uprobe_get_trap_addr(regs));
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exit:
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@ -30,6 +30,7 @@
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#include <asm/cpu_entry_area.h> /* exception stack */
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#include <asm/pgtable_areas.h> /* VMALLOC_START, ... */
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#include <asm/kvm_para.h> /* kvm_handle_async_pf */
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#include <asm/vdso.h> /* fixup_vdso_exception() */
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#define CREATE_TRACE_POINTS
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#include <asm/trace/exceptions.h>
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@ -814,6 +815,9 @@ __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
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sanitize_error_code(address, &error_code);
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if (fixup_vdso_exception(regs, X86_TRAP_PF, error_code, address))
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return;
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if (likely(show_unhandled_signals))
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show_signal_msg(regs, error_code, address, tsk);
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@ -933,6 +937,9 @@ do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address,
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sanitize_error_code(address, &error_code);
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if (fixup_vdso_exception(regs, X86_TRAP_PF, error_code, address))
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return;
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set_signal_archinfo(address, error_code);
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#ifdef CONFIG_MEMORY_FAILURE
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