diff options
Diffstat (limited to '0078-x86-nospec-Fix-evaluate_nospec-code-generation-under.patch')
| -rw-r--r-- | 0078-x86-nospec-Fix-evaluate_nospec-code-generation-under.patch | 101 |
1 files changed, 0 insertions, 101 deletions
diff --git a/0078-x86-nospec-Fix-evaluate_nospec-code-generation-under.patch b/0078-x86-nospec-Fix-evaluate_nospec-code-generation-under.patch deleted file mode 100644 index 62de15a..0000000 --- a/0078-x86-nospec-Fix-evaluate_nospec-code-generation-under.patch +++ /dev/null @@ -1,101 +0,0 @@ -From 00aa5c93d14c6561a69fe204cbe29f7519830782 Mon Sep 17 00:00:00 2001 -From: Andrew Cooper <andrew.cooper3@citrix.com> -Date: Fri, 31 Mar 2023 08:31:20 +0200 -Subject: [PATCH 78/89] x86/nospec: Fix evaluate_nospec() code generation under - Clang -MIME-Version: 1.0 -Content-Type: text/plain; charset=UTF-8 -Content-Transfer-Encoding: 8bit - -It turns out that evaluate_nospec() code generation is not safe under Clang. -Given: - - void eval_nospec_test(int x) - { - if ( evaluate_nospec(x) ) - asm volatile ("nop #true" ::: "memory"); - else - asm volatile ("nop #false" ::: "memory"); - } - -Clang emits: - - <eval_nospec_test>: - 0f ae e8 lfence - 85 ff test %edi,%edi - 74 02 je <eval_nospec_test+0x9> - 90 nop - c3 ret - 90 nop - c3 ret - -which is not safe because the lfence has been hoisted above the conditional -jump. Clang concludes that both barrier_nospec_true()'s have identical side -effects and can safely be merged. - -Clang can be persuaded that the side effects are different if there are -different comments in the asm blocks. This is fragile, but no more fragile -that other aspects of this construct. - -Introduce barrier_nospec_false() with a separate internal comment to prevent -Clang merging it with barrier_nospec_true() despite the otherwise-identical -content. The generated code now becomes: - - <eval_nospec_test>: - 85 ff test %edi,%edi - 74 05 je <eval_nospec_test+0x9> - 0f ae e8 lfence - 90 nop - c3 ret - 0f ae e8 lfence - 90 nop - c3 ret - -which has the correct number of lfence's, and in the correct place. - -Link: https://github.com/llvm/llvm-project/issues/55084 -Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> -Reviewed-by: Roger Pau Monné <roger.pau@citrix.com> -Reviewed-by: Jan Beulich <jbeulich@suse.com> -master commit: bc3c133841435829ba5c0a48427e2a77633502ab -master date: 2023-03-24 12:16:31 +0000 ---- - xen/arch/x86/include/asm/nospec.h | 15 +++++++++++++-- - 1 file changed, 13 insertions(+), 2 deletions(-) - -diff --git a/xen/arch/x86/include/asm/nospec.h b/xen/arch/x86/include/asm/nospec.h -index 5312ae4c6f..7150e76b87 100644 ---- a/xen/arch/x86/include/asm/nospec.h -+++ b/xen/arch/x86/include/asm/nospec.h -@@ -10,15 +10,26 @@ - static always_inline bool barrier_nospec_true(void) - { - #ifdef CONFIG_SPECULATIVE_HARDEN_BRANCH -- alternative("lfence", "", X86_FEATURE_SC_NO_BRANCH_HARDEN); -+ alternative("lfence #nospec-true", "", X86_FEATURE_SC_NO_BRANCH_HARDEN); - #endif - return true; - } - -+static always_inline bool barrier_nospec_false(void) -+{ -+#ifdef CONFIG_SPECULATIVE_HARDEN_BRANCH -+ alternative("lfence #nospec-false", "", X86_FEATURE_SC_NO_BRANCH_HARDEN); -+#endif -+ return false; -+} -+ - /* Allow to protect evaluation of conditionals with respect to speculation */ - static always_inline bool evaluate_nospec(bool condition) - { -- return condition ? barrier_nospec_true() : !barrier_nospec_true(); -+ if ( condition ) -+ return barrier_nospec_true(); -+ else -+ return barrier_nospec_false(); - } - - /* Allow to block speculative execution in generic code */ --- -2.40.0 - |