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commitfe83f5eae4upstream. The commit in Fixes started adding INT3 after RETs as a mitigation against straight-line speculation. The fastop SETcc implementation in kvm's insn emulator uses macro magic to generate all possible SETcc functions and to jump to them when emulating the respective instruction. However, it hardcodes the size and alignment of those functions to 4: a three-byte SETcc insn and a single-byte RET. BUT, with SLS, there's an INT3 that gets slapped after the RET, which brings the whole scheme out of alignment: 15: 0f 90 c0 seto %al 18: c3 ret 19: cc int3 1a: 0f 1f 00 nopl (%rax) 1d: 0f 91 c0 setno %al 20: c3 ret 21: cc int3 22: 0f 1f 00 nopl (%rax) 25: 0f 92 c0 setb %al 28: c3 ret 29: cc int3 and this explodes like this: int3: 0000 [#1] PREEMPT SMP PTI CPU: 0 PID: 2435 Comm: qemu-system-x86 Not tainted 5.17.0-rc8-sls #1 Hardware name: Dell Inc. Precision WorkStation T3400 /0TP412, BIOS A14 04/30/2012 RIP: 0010:setc+0x5/0x8 [kvm] Code: 00 00 0f 1f 00 0f b6 05 43 24 06 00 c3 cc 0f 1f 80 00 00 00 00 0f 90 c0 c3 cc 0f \ 1f 00 0f 91 c0 c3 cc 0f 1f 00 0f 92 c0 c3 cc <0f> 1f 00 0f 93 c0 c3 cc 0f 1f 00 \ 0f 94 c0 c3 cc 0f 1f 00 0f 95 c0 Call Trace: <TASK> ? x86_emulate_insn [kvm] ? x86_emulate_instruction [kvm] ? vmx_handle_exit [kvm_intel] ? kvm_arch_vcpu_ioctl_run [kvm] ? kvm_vcpu_ioctl [kvm] ? __x64_sys_ioctl ? do_syscall_64 ? entry_SYSCALL_64_after_hwframe </TASK> Raise the alignment value when SLS is enabled and use a macro for that instead of hard-coding naked numbers. Fixes:e463a09af2("x86: Add straight-line-speculation mitigation") Reported-by: Jamie Heilman <jamie@audible.transient.net> Signed-off-by: Borislav Petkov <bp@suse.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Tested-by: Jamie Heilman <jamie@audible.transient.net> Link: https://lore.kernel.org/r/YjGzJwjrvxg5YZ0Z@audible.transient.net [Add a comment and a bit of safety checking, since this is going to be changed again for IBT support. - Paolo] Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.