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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:63305e5392("x86/spec-ctrl: Mitigate Cross-Thread Return Address Predictions") Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> Reviewed-by: Jan Beulich <jbeulich@suse.com> master commit:a2adacff0bmaster date: 2023-02-24 17:44:29 +0000
This commit is contained in:
Andrew Cooper authored and Jan Beulich committed
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700320a792
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2b8f72a6b4
2 files changed
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-11
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@@ -83,7 +83,7 @@ static always_inline void spec_ctrl_new_guest_context(void)
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wrmsrl(MSR_PRED_CMD, PRED_CMD_IBPB);
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/* (ab)use alternative_input() to specify clobbers. */
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alternative_input("", "DO_OVERWRITE_RSB", X86_BUG_IBPB_NO_RET,
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alternative_input("", "DO_OVERWRITE_RSB xu=%=", X86_BUG_IBPB_NO_RET,
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: "rax", "rcx");
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}
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@@ -172,7 +172,7 @@ static always_inline void spec_ctrl_enter_idle(struct cpu_info *info)
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*
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* (ab)use alternative_input() to specify clobbers.
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*/
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alternative_input("", "DO_OVERWRITE_RSB", X86_FEATURE_SC_RSB_IDLE,
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alternative_input("", "DO_OVERWRITE_RSB xu=%=", X86_FEATURE_SC_RSB_IDLE,
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: "rax", "rcx");
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}
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@@ -117,11 +117,16 @@
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.L\@_done:
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.endm
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.macro DO_OVERWRITE_RSB tmp=rax
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.macro DO_OVERWRITE_RSB tmp=rax xu
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/*
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* Requires nothing
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* Clobbers \tmp (%rax by default), %rcx
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*
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* xu is an optional parameter to add eXtra Uniqueness. It is intended for
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* passing %= in from an asm() block, in order to work around
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* https://github.com/llvm/llvm-project/issues/60792 where Clang-IAS doesn't
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* expand \@ uniquely.
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*
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* Requires 256 bytes of {,shadow}stack space, but %rsp/SSP has no net
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* change. Based on Google's performance numbers, the loop is unrolled to 16
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* iterations and two calls per iteration.
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@@ -137,31 +142,31 @@
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mov $16, %ecx /* 16 iterations, two calls per loop */
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mov %rsp, %\tmp /* Store the current %rsp */
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.L\@_fill_rsb_loop:
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.L\@_fill_rsb_loop\xu:
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.irp n, 1, 2 /* Unrolled twice. */
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call .L\@_insert_rsb_entry_\n /* Create an RSB entry. */
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call .L\@_insert_rsb_entry\xu\n /* Create an RSB entry. */
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.L\@_capture_speculation_\n:
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.L\@_capture_speculation\xu\n:
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pause
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lfence
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jmp .L\@_capture_speculation_\n /* Capture rogue speculation. */
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jmp .L\@_capture_speculation\xu\n /* Capture rogue speculation. */
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.L\@_insert_rsb_entry_\n:
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.L\@_insert_rsb_entry\xu\n:
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.endr
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sub $1, %ecx
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jnz .L\@_fill_rsb_loop
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jnz .L\@_fill_rsb_loop\xu
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mov %\tmp, %rsp /* Restore old %rsp */
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#ifdef CONFIG_XEN_SHSTK
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mov $1, %ecx
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rdsspd %ecx
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cmp $1, %ecx
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je .L\@_shstk_done
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je .L\@_shstk_done\xu
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mov $64, %ecx /* 64 * 4 bytes, given incsspd */
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incsspd %ecx /* Restore old SSP */
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.L\@_shstk_done:
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.L\@_shstk_done\xu:
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#endif
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.endm
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