69712baf24
commit f58d6fbcb7c848b7f2469be339bc571f2e9d245b upstream.
Initially, it was thought that doing an innocuous division in the #DE
handler would take care to prevent any leaking of old data from the
divider but by the time the fault is raised, the speculation has already
advanced too far and such data could already have been used by younger
operations.
Therefore, do the innocuous division on every exit to userspace so that
userspace doesn't see any potentially old data from integer divisions in
kernel space.
Do the same before VMRUN too, to protect host data from leaking into the
guest too.
Fixes: 77245f1c3c64 ("x86/CPU/AMD: Do not leak quotient data after a division by 0")
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Cc: <stable@kernel.org>
Link: https://lore.kernel.org/r/20230811213824.10025-1-bp@alien8.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
86 lines
2.5 KiB
C
86 lines
2.5 KiB
C
/* SPDX-License-Identifier: GPL-2.0-only */
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#ifndef _ASM_X86_ENTRY_COMMON_H
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#define _ASM_X86_ENTRY_COMMON_H
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#include <linux/user-return-notifier.h>
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#include <asm/nospec-branch.h>
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#include <asm/io_bitmap.h>
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#include <asm/fpu/api.h>
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/* Check that the stack and regs on entry from user mode are sane. */
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static __always_inline void arch_check_user_regs(struct pt_regs *regs)
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{
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if (IS_ENABLED(CONFIG_DEBUG_ENTRY)) {
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/*
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* Make sure that the entry code gave us a sensible EFLAGS
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* register. Native because we want to check the actual CPU
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* state, not the interrupt state as imagined by Xen.
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*/
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unsigned long flags = native_save_fl();
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unsigned long mask = X86_EFLAGS_DF | X86_EFLAGS_NT;
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/*
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* For !SMAP hardware we patch out CLAC on entry.
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*/
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if (boot_cpu_has(X86_FEATURE_SMAP) ||
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(IS_ENABLED(CONFIG_64BIT) && boot_cpu_has(X86_FEATURE_XENPV)))
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mask |= X86_EFLAGS_AC;
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WARN_ON_ONCE(flags & mask);
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/* We think we came from user mode. Make sure pt_regs agrees. */
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WARN_ON_ONCE(!user_mode(regs));
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/*
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* All entries from user mode (except #DF) should be on the
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* normal thread stack and should have user pt_regs in the
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* correct location.
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*/
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WARN_ON_ONCE(!on_thread_stack());
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WARN_ON_ONCE(regs != task_pt_regs(current));
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}
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}
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#define arch_check_user_regs arch_check_user_regs
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#define ARCH_SYSCALL_EXIT_WORK (_TIF_SINGLESTEP)
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static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,
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unsigned long ti_work)
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{
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if (ti_work & _TIF_USER_RETURN_NOTIFY)
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fire_user_return_notifiers();
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if (unlikely(ti_work & _TIF_IO_BITMAP))
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tss_update_io_bitmap();
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fpregs_assert_state_consistent();
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if (unlikely(ti_work & _TIF_NEED_FPU_LOAD))
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switch_fpu_return();
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#ifdef CONFIG_COMPAT
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/*
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* Compat syscalls set TS_COMPAT. Make sure we clear it before
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* returning to user mode. We need to clear it *after* signal
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* handling, because syscall restart has a fixup for compat
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* syscalls. The fixup is exercised by the ptrace_syscall_32
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* selftest.
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*
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* We also need to clear TS_REGS_POKED_I386: the 32-bit tracer
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* special case only applies after poking regs and before the
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* very next return to user mode.
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*/
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current_thread_info()->status &= ~(TS_COMPAT | TS_I386_REGS_POKED);
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#endif
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}
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#define arch_exit_to_user_mode_prepare arch_exit_to_user_mode_prepare
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static __always_inline void arch_exit_to_user_mode(void)
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{
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mds_user_clear_cpu_buffers();
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amd_clear_divider();
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}
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#define arch_exit_to_user_mode arch_exit_to_user_mode
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#endif
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