[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [xen master] xen: Work around Clang-IAS macro \@ expansion bug
commit a2adacff0b91cc7b977abb209dc419a2ef15963f Author: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> AuthorDate: Fri Feb 17 00:12:24 2023 +0000 Commit: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> CommitDate: Fri Feb 24 17:44:29 2023 +0000 xen: Work around Clang-IAS macro \@ expansion bug https://github.com/llvm/llvm-project/issues/60792 It turns out that Clang-IAS does not expand \@ uniquely in a translaition unit, and the XSA-426 change tickles this bug: <instantiation>:4:1: error: invalid symbol redefinition .L1_fill_rsb_loop: ^ make[3]: *** [Rules.mk:247: arch/x86/acpi/cpu_idle.o] Error 1 Extend DO_OVERWRITE_RSB with an optional parameter so C callers can mix %= in too, which Clang does seem to expand properly. Fixes: 63305e5392ec ("x86/spec-ctrl: Mitigate Cross-Thread Return Address Predictions") Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx> --- xen/arch/x86/include/asm/spec_ctrl.h | 4 ++-- xen/arch/x86/include/asm/spec_ctrl_asm.h | 19 ++++++++++++------- 2 files changed, 14 insertions(+), 9 deletions(-) diff --git a/xen/arch/x86/include/asm/spec_ctrl.h b/xen/arch/x86/include/asm/spec_ctrl.h index 3cf8a7d304..f718f94088 100644 --- a/xen/arch/x86/include/asm/spec_ctrl.h +++ b/xen/arch/x86/include/asm/spec_ctrl.h @@ -83,7 +83,7 @@ static always_inline void spec_ctrl_new_guest_context(void) wrmsrl(MSR_PRED_CMD, PRED_CMD_IBPB); /* (ab)use alternative_input() to specify clobbers. */ - alternative_input("", "DO_OVERWRITE_RSB", X86_BUG_IBPB_NO_RET, + alternative_input("", "DO_OVERWRITE_RSB xu=%=", X86_BUG_IBPB_NO_RET, : "rax", "rcx"); } @@ -172,7 +172,7 @@ static always_inline void spec_ctrl_enter_idle(struct cpu_info *info) * * (ab)use alternative_input() to specify clobbers. */ - alternative_input("", "DO_OVERWRITE_RSB", X86_FEATURE_SC_RSB_IDLE, + alternative_input("", "DO_OVERWRITE_RSB xu=%=", X86_FEATURE_SC_RSB_IDLE, : "rax", "rcx"); } diff --git a/xen/arch/x86/include/asm/spec_ctrl_asm.h b/xen/arch/x86/include/asm/spec_ctrl_asm.h index fab27ff553..f23bb105c5 100644 --- a/xen/arch/x86/include/asm/spec_ctrl_asm.h +++ b/xen/arch/x86/include/asm/spec_ctrl_asm.h @@ -117,11 +117,16 @@ .L\@_done: .endm -.macro DO_OVERWRITE_RSB tmp=rax +.macro DO_OVERWRITE_RSB tmp=rax xu /* * Requires nothing * Clobbers \tmp (%rax by default), %rcx * + * xu is an optional parameter to add eXtra Uniqueness. It is intended for + * passing %= in from an asm() block, in order to work around + * https://github.com/llvm/llvm-project/issues/60792 where Clang-IAS doesn't + * expand \@ uniquely. + * * Requires 256 bytes of {,shadow}stack space, but %rsp/SSP has no net * change. Based on Google's performance numbers, the loop is unrolled to 16 * iterations and two calls per iteration. @@ -136,27 +141,27 @@ mov $16, %ecx /* 16 iterations, two calls per loop */ mov %rsp, %\tmp /* Store the current %rsp */ -.L\@_fill_rsb_loop: +.L\@_fill_rsb_loop\xu: .irp n, 1, 2 /* Unrolled twice. */ - call .L\@_insert_rsb_entry_\n /* Create an RSB entry. */ + call .L\@_insert_rsb_entry\xu\n /* Create an RSB entry. */ int3 /* Halt rogue speculation. */ -.L\@_insert_rsb_entry_\n: +.L\@_insert_rsb_entry\xu\n: .endr sub $1, %ecx - jnz .L\@_fill_rsb_loop + jnz .L\@_fill_rsb_loop\xu mov %\tmp, %rsp /* Restore old %rsp */ #ifdef CONFIG_XEN_SHSTK mov $1, %ecx rdsspd %ecx cmp $1, %ecx - je .L\@_shstk_done + je .L\@_shstk_done\xu mov $64, %ecx /* 64 * 4 bytes, given incsspd */ incsspd %ecx /* Restore old SSP */ -.L\@_shstk_done: +.L\@_shstk_done\xu: #endif .endm -- generated by git-patchbot for /home/xen/git/xen.git#master
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