x86/retpoline: Simplify retpolines
stable inclusion from stable-v5.10.133 commit 28ca351296742a9e7506a548acaf7ea3bc9feef0 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I5PTAS CVE: CVE-2022-29900,CVE-2022-23816,CVE-2022-29901 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=28ca351296742a9e7506a548acaf7ea3bc9feef0 -------------------------------- commit 11925185 upstream. Due to: c9c324dc ("objtool: Support stack layout changes in alternatives") it is now possible to simplify the retpolines. Currently our retpolines consist of 2 symbols: - __x86_indirect_thunk_\reg: the compiler target - __x86_retpoline_\reg: the actual retpoline. Both are consecutive in code and aligned such that for any one register they both live in the same cacheline: 0000000000000000 <__x86_indirect_thunk_rax>: 0: ff e0 jmpq *%rax 2: 90 nop 3: 90 nop 4: 90 nop 0000000000000005 <__x86_retpoline_rax>: 5: e8 07 00 00 00 callq 11 <__x86_retpoline_rax+0xc> a: f3 90 pause c: 0f ae e8 lfence f: eb f9 jmp a <__x86_retpoline_rax+0x5> 11: 48 89 04 24 mov %rax,(%rsp) 15: c3 retq 16: 66 2e 0f 1f 84 00 00 00 00 00 nopw %cs:0x0(%rax,%rax,1) The thunk is an alternative_2, where one option is a JMP to the retpoline. This was done so that objtool didn't need to deal with alternatives with stack ops. But that problem has been solved, so now it is possible to fold the entire retpoline into the alternative to simplify and consolidate unused bytes: 0000000000000000 <__x86_indirect_thunk_rax>: 0: ff e0 jmpq *%rax 2: 90 nop 3: 90 nop 4: 90 nop 5: 90 nop 6: 90 nop 7: 90 nop 8: 90 nop 9: 90 nop a: 90 nop b: 90 nop c: 90 nop d: 90 nop e: 90 nop f: 90 nop 10: 90 nop 11: 66 66 2e 0f 1f 84 00 00 00 00 00 data16 nopw %cs:0x0(%rax,%rax,1) 1c: 0f 1f 40 00 nopl 0x0(%rax) Notice that since the longest alternative sequence is now: 0: e8 07 00 00 00 callq c <.altinstr_replacement+0xc> 5: f3 90 pause 7: 0f ae e8 lfence a: eb f9 jmp 5 <.altinstr_replacement+0x5> c: 48 89 04 24 mov %rax,(%rsp) 10: c3 retq 17 bytes, we have 15 bytes NOP at the end of our 32 byte slot. (IOW, if we can shrink the retpoline by 1 byte we can pack it more densely). [ bp: Massage commit message. ] Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: NBorislav Petkov <bp@suse.de> Signed-off-by: NIngo Molnar <mingo@kernel.org> Link: https://lkml.kernel.org/r/20210326151259.506071949@infradead.org [bwh: Backported to 5.10: - Use X86_FEATRURE_RETPOLINE_LFENCE flag instead of X86_FEATURE_RETPOLINE_AMD, since the later renaming of this flag has already been applied - Adjust context] Signed-off-by: NBen Hutchings <ben@decadent.org.uk> Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: NLin Yujun <linyujun809@huawei.com> Reviewed-by: NZhang Jianhua <chris.zjh@huawei.com> Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>
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