arm64: Mitigate spectre style branch history side channels
stable inclusion from stable-v5.10.105 commit e192c8baa69ac8a5585d61ac535aa1e5eb795e80 category: bugfix bugzilla: 186460 https://gitee.com/src-openeuler/kernel/issues/I53MHA CVE: CVE-2022-23960 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e192c8baa69a -------------------------------- commit 558c303c upstream. Speculation attacks against some high-performance processors can make use of branch history to influence future speculation. When taking an exception from user-space, a sequence of branches or a firmware call overwrites or invalidates the branch history. The sequence of branches is added to the vectors, and should appear before the first indirect branch. For systems using KPTI the sequence is added to the kpti trampoline where it has a free register as the exit from the trampoline is via a 'ret'. For systems not using KPTI, the same register tricks are used to free up a register in the vectors. For the firmware call, arch-workaround-3 clobbers 4 registers, so there is no choice but to save them to the EL1 stack. This only happens for entry from EL0, so if we take an exception due to the stack access, it will not become re-entrant. For KVM, the existing branch-predictor-hardening vectors are used. When a spectre version of these vectors is in use, the firmware call is sufficient to mitigate against Spectre-BHB. For the non-spectre versions, the sequence of branches is added to the indirect vector. Reviewed-by: NCatalin Marinas <catalin.marinas@arm.com> [ modified for stable, removed bitmap of mitigations, use kvm template infrastructure ] Signed-off-by: NJames Morse <james.morse@arm.com> Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: NChen Jiahao <chenjiahao16@huawei.com> Reviewed-by: NLiao Chang <liaochang1@huawei.com> Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>
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