kernel/linux.git/arch/x86/entry, branch v5.10.257

x86/vsyscall: Do not require X86_PF_INSTR to emulate vsyscall

2025-12-06T21:08:11+00:00

[ Upstream commit 8ba38a7a9a699905b84fa97578a8291010dec273 ] emulate_vsyscall() expects to see X86_PF_INSTR in PFEC on a vsyscall page fault, but the CPU does not report X86_PF_INSTR if neither X86_FEATURE_NX nor X86_FEATURE_SMEP are enabled. X86_FEATURE_NX should be enabled on nearly all 64-bit CPUs, except for early P4 processors that did not support this feature. Instead of explicitly checking for X86_PF_INSTR, compare the fault address to RIP. On machines with X86_FEATURE_NX enabled, issue a warning if RIP is equal to fault address but X86_PF_INSTR is absent. [ dhansen: flesh out code comments ] Originally-by: Dave Hansen Reported-by: Andrew Cooper Signed-off-by: Kirill A. Shutemov Signed-off-by: Dave Hansen Reviewed-by: Andrew Cooper Link: https://lore.kernel.org/all/bd81a98b-f8d4-4304-ac55-d4151a1a77ab@intel.com Link: https://lore.kernel.org/all/20250624145918.2720487-1-kirill.shutemov%40linux.intel.com Signed-off-by: Sasha Levin

x86/bugs: Rename MDS machinery to something more generic

2025-07-17T16:28:00+00:00

From: "Borislav Petkov (AMD)" Commit f9af88a3d384c8b55beb5dc5483e5da0135fadbd upstream. It will be used by other x86 mitigations. No functional changes. Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Pawan Gupta Signed-off-by: Greg Kroah-Hartman

x86/bugs: Use SBPB in write_ibpb() if applicable

2025-05-02T05:41:20+00:00

[ Upstream commit fc9fd3f98423367c79e0bd85a9515df26dc1b3cc ] write_ibpb() does IBPB, which (among other things) flushes branch type predictions on AMD. If the CPU has SRSO_NO, or if the SRSO mitigation has been disabled, branch type flushing isn't needed, in which case the lighter-weight SBPB can be used. The 'x86_pred_cmd' variable already keeps track of whether IBPB or SBPB should be used. Use that instead of hardcoding IBPB. Signed-off-by: Josh Poimboeuf Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/17c5dcd14b29199b75199d67ff7758de9d9a4928.1744148254.git.jpoimboe@kernel.org Signed-off-by: Sasha Levin

x86/entry: Fix ORC unwinder for PUSH_REGS with save_ret=1

2025-04-10T12:30:58+00:00

[ Upstream commit 57e2428f8df8263275344566e02c277648a4b7f1 ] PUSH_REGS with save_ret=1 is used by interrupt entry helper functions that initially start with a UNWIND_HINT_FUNC ORC state. However, save_ret=1 means that we clobber the helper function's return address (and then later restore the return address further down on the stack); after that point, the only thing on the stack we can unwind through is the IRET frame, so use UNWIND_HINT_IRET_REGS until we have a full pt_regs frame. ( An alternate approach would be to move the pt_regs->di overwrite down such that it is the final step of pt_regs setup; but I don't want to rearrange entry code just to make unwinding a tiny bit more elegant. ) Fixes: 9e809d15d6b6 ("x86/entry: Reduce the code footprint of the 'idtentry' macro") Signed-off-by: Jann Horn Signed-off-by: Ingo Molnar Cc: Andy Lutomirski Cc: Brian Gerst Cc: Juergen Gross Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Kees Cook Cc: Peter Zijlstra Cc: Josh Poimboeuf Link: https://lore.kernel.org/r/20250325-2025-03-unwind-fixes-v1-1-acd774364768@google.com Signed-off-by: Sasha Levin

x86/entry_32: Clear CPU buffers after register restore in NMI return

2024-10-22T13:39:29+00:00

commit 48a2440d0f20c826b884e04377ccc1e4696c84e9 upstream. CPU buffers are currently cleared after call to exc_nmi, but before register state is restored. This may be okay for MDS mitigation but not for RDFS. Because RDFS mitigation requires CPU buffers to be cleared when registers don't have any sensitive data. Move CLEAR_CPU_BUFFERS after RESTORE_ALL_NMI. Fixes: a0e2dab44d22 ("x86/entry_32: Add VERW just before userspace transition") Suggested-by: Dave Hansen Signed-off-by: Pawan Gupta Signed-off-by: Dave Hansen Cc:stable@vger.kernel.org Link: https://lore.kernel.org/all/20240925-fix-dosemu-vm86-v7-2-1de0daca2d42%40linux.intel.com Signed-off-by: Greg Kroah-Hartman

x86/entry_32: Do not clobber user EFLAGS.ZF

2024-10-22T13:39:29+00:00

commit 2e2e5143d4868163d6756c8c6a4d28cbfa5245e5 upstream. Opportunistic SYSEXIT executes VERW to clear CPU buffers after user EFLAGS are restored. This can clobber user EFLAGS.ZF. Move CLEAR_CPU_BUFFERS before the user EFLAGS are restored. This ensures that the user EFLAGS.ZF is not clobbered. Closes: https://lore.kernel.org/lkml/yVXwe8gvgmPADpRB6lXlicS2fcHoV5OHHxyuFbB_MEleRPD7-KhGe5VtORejtPe-KCkT8Uhcg5d7-IBw4Ojb4H7z5LQxoZylSmJ8KNL3A8o=@protonmail.com/ Fixes: a0e2dab44d22 ("x86/entry_32: Add VERW just before userspace transition") Reported-by: Jari Ruusu Signed-off-by: Pawan Gupta Signed-off-by: Dave Hansen Cc:stable@vger.kernel.org Link: https://lore.kernel.org/all/20240925-fix-dosemu-vm86-v7-1-1de0daca2d42%40linux.intel.com Signed-off-by: Greg Kroah-Hartman

x86/entry: Have entry_ibpb() invalidate return predictions

2024-10-22T13:39:26+00:00

commit 50e4b3b94090babe8d4bb85c95f0d3e6b07ea86e upstream. entry_ibpb() should invalidate all indirect predictions, including return target predictions. Not all IBPB implementations do this, in which case the fallback is RSB filling. Prevent SRSO-style hijacks of return predictions following IBPB, as the return target predictor can be corrupted before the IBPB completes. [ bp: Massage. ] Signed-off-by: Johannes Wikner Signed-off-by: Borislav Petkov (AMD) Cc: Signed-off-by: Greg Kroah-Hartman

syscalls: fix compat_sys_io_pgetevents_time64 usage

2024-07-05T07:12:55+00:00

commit d3882564a77c21eb746ba5364f3fa89b88de3d61 upstream. Using sys_io_pgetevents() as the entry point for compat mode tasks works almost correctly, but misses the sign extension for the min_nr and nr arguments. This was addressed on parisc by switching to compat_sys_io_pgetevents_time64() in commit 6431e92fc827 ("parisc: io_pgetevents_time64() needs compat syscall in 32-bit compat mode"), as well as by using more sophisticated system call wrappers on x86 and s390. However, arm64, mips, powerpc, sparc and riscv still have the same bug. Change all of them over to use compat_sys_io_pgetevents_time64() like parisc already does. This was clearly the intention when the function was originally added, but it got hooked up incorrectly in the tables. Cc: stable@vger.kernel.org Fixes: 48166e6ea47d ("y2038: add 64-bit time_t syscalls to all 32-bit architectures") Acked-by: Heiko Carstens # s390 Signed-off-by: Arnd Bergmann Signed-off-by: Greg Kroah-Hartman

x86/mm: Remove broken vsyscall emulation code from the page fault code

2024-06-16T11:32:31+00:00

commit 02b670c1f88e78f42a6c5aee155c7b26960ca054 upstream. The syzbot-reported stack trace from hell in this discussion thread actually has three nested page faults: https://lore.kernel.org/r/000000000000d5f4fc0616e816d4@google.com ... and I think that's actually the important thing here: - the first page fault is from user space, and triggers the vsyscall emulation. - the second page fault is from __do_sys_gettimeofday(), and that should just have caused the exception that then sets the return value to -EFAULT - the third nested page fault is due to _raw_spin_unlock_irqrestore() -> preempt_schedule() -> trace_sched_switch(), which then causes a BPF trace program to run, which does that bpf_probe_read_compat(), which causes that page fault under pagefault_disable(). It's quite the nasty backtrace, and there's a lot going on. The problem is literally the vsyscall emulation, which sets current->thread.sig_on_uaccess_err = 1; and that causes the fixup_exception() code to send the signal *despite* the exception being caught. And I think that is in fact completely bogus. It's completely bogus exactly because it sends that signal even when it *shouldn't* be sent - like for the BPF user mode trace gathering. In other words, I think the whole "sig_on_uaccess_err" thing is entirely broken, because it makes any nested page-faults do all the wrong things. Now, arguably, I don't think anybody should enable vsyscall emulation any more, but this test case clearly does. I think we should just make the "send SIGSEGV" be something that the vsyscall emulation does on its own, not this broken per-thread state for something that isn't actually per thread. The x86 page fault code actually tried to deal with the "incorrect nesting" by having that: if (in_interrupt()) return; which ignores the sig_on_uaccess_err case when it happens in interrupts, but as shown by this example, these nested page faults do not need to be about interrupts at all. IOW, I think the only right thing is to remove that horrendously broken code. The attached patch looks like the ObviouslyCorrect(tm) thing to do. NOTE! This broken code goes back to this commit in 2011: 4fc3490114bb ("x86-64: Set siginfo and context on vsyscall emulation faults") ... and back then the reason was to get all the siginfo details right. Honestly, I do not for a moment believe that it's worth getting the siginfo details right here, but part of the commit says: This fixes issues with UML when vsyscall=emulate. ... and so my patch to remove this garbage will probably break UML in this situation. I do not believe that anybody should be running with vsyscall=emulate in 2024 in the first place, much less if you are doing things like UML. But let's see if somebody screams. Reported-and-tested-by: syzbot+83e7f982ca045ab4405c@syzkaller.appspotmail.com Signed-off-by: Linus Torvalds Signed-off-by: Ingo Molnar Tested-by: Jiri Olsa Acked-by: Andy Lutomirski Link: https://lore.kernel.org/r/CAHk-=wh9D6f7HUkDgZHKmDCHUQmp+Co89GP+b8+z+G56BKeyNg@mail.gmail.com Signed-off-by: Sasha Levin [gpiccoli: Backport the patch due to differences in the trees. The main change between 5.10.y and 5.15.y is due to renaming the fixup function, by commit 6456a2a69ee1 ("x86/fault: Rename no_context() to kernelmode_fixup_or_oops()"). Following 2 commits cause divergence in the diffs too (in the removed lines): cd072dab453a ("x86/fault: Add a helper function to sanitize error code") d4ffd5df9d18 ("x86/fault: Fix wrong signal when vsyscall fails with pkey") Finally, there is context adjustment in the processor.h file.] Signed-off-by: Guilherme G. Piccoli Signed-off-by: Greg Kroah-Hartman

x86/xen: Drop USERGS_SYSRET64 paravirt call

2024-05-25T14:19:05+00:00

commit afd30525a659ac0ae0904f0cb4a2ca75522c3123 upstream. USERGS_SYSRET64 is used to return from a syscall via SYSRET, but a Xen PV guest will nevertheless use the IRET hypercall, as there is no sysret PV hypercall defined. So instead of testing all the prerequisites for doing a sysret and then mangling the stack for Xen PV again for doing an iret just use the iret exit from the beginning. This can easily be done via an ALTERNATIVE like it is done for the sysenter compat case already. It should be noted that this drops the optimization in Xen for not restoring a few registers when returning to user mode, but it seems as if the saved instructions in the kernel more than compensate for this drop (a kernel build in a Xen PV guest was slightly faster with this patch applied). While at it remove the stale sysret32 remnants. [ pawan: Brad Spengler and Salvatore Bonaccorso reported a problem with the 5.10 backport commit edc702b4a820 ("x86/entry_64: Add VERW just before userspace transition"). When CONFIG_PARAVIRT_XXL=y, CLEAR_CPU_BUFFERS is not executed in syscall_return_via_sysret path as USERGS_SYSRET64 is runtime patched to: .cpu_usergs_sysret64 = { 0x0f, 0x01, 0xf8, 0x48, 0x0f, 0x07 }, // swapgs; sysretq which is missing CLEAR_CPU_BUFFERS. It turns out dropping USERGS_SYSRET64 simplifies the code, allowing CLEAR_CPU_BUFFERS to be explicitly added to syscall_return_via_sysret path. Below is with CONFIG_PARAVIRT_XXL=y and this patch applied: syscall_return_via_sysret: ... <+342>: swapgs <+345>: xchg %ax,%ax <+347>: verw -0x1a2(%rip) <------ <+354>: sysretq ] Signed-off-by: Juergen Gross Signed-off-by: Borislav Petkov Signed-off-by: Pawan Gupta Link: https://lkml.kernel.org/r/20210120135555.32594-6-jgross@suse.com Signed-off-by: Greg Kroah-Hartman