diff options
Diffstat (limited to 'common/recipes-kernel/linux/linux-yocto-4.9.21/0080-x86-retpoline-Add-LFENCE-to-the-retpoline-RSB-fillin.patch')
| -rw-r--r-- | common/recipes-kernel/linux/linux-yocto-4.9.21/0080-x86-retpoline-Add-LFENCE-to-the-retpoline-RSB-fillin.patch | 94 |
1 files changed, 94 insertions, 0 deletions
diff --git a/common/recipes-kernel/linux/linux-yocto-4.9.21/0080-x86-retpoline-Add-LFENCE-to-the-retpoline-RSB-fillin.patch b/common/recipes-kernel/linux/linux-yocto-4.9.21/0080-x86-retpoline-Add-LFENCE-to-the-retpoline-RSB-fillin.patch new file mode 100644 index 00000000..acb54587 --- /dev/null +++ b/common/recipes-kernel/linux/linux-yocto-4.9.21/0080-x86-retpoline-Add-LFENCE-to-the-retpoline-RSB-fillin.patch @@ -0,0 +1,94 @@ +From b72091ebb94e5cb7808c813989e6b5aefa464751 Mon Sep 17 00:00:00 2001 +From: Tom Lendacky <thomas.lendacky@amd.com> +Date: Sat, 13 Jan 2018 17:27:30 -0600 +Subject: [PATCH 080/103] x86/retpoline: Add LFENCE to the retpoline/RSB + filling RSB macros + +commit 28d437d550e1e39f805d99f9f8ac399c778827b7 upstream. + +The PAUSE instruction is currently used in the retpoline and RSB filling +macros as a speculation trap. The use of PAUSE was originally suggested +because it showed a very, very small difference in the amount of +cycles/time used to execute the retpoline as compared to LFENCE. On AMD, +the PAUSE instruction is not a serializing instruction, so the pause/jmp +loop will use excess power as it is speculated over waiting for return +to mispredict to the correct target. + +The RSB filling macro is applicable to AMD, and, if software is unable to +verify that LFENCE is serializing on AMD (possible when running under a +hypervisor), the generic retpoline support will be used and, so, is also +applicable to AMD. Keep the current usage of PAUSE for Intel, but add an +LFENCE instruction to the speculation trap for AMD. + +The same sequence has been adopted by GCC for the GCC generated retpolines. + +Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com> +Signed-off-by: Thomas Gleixner <tglx@linutronix.de> +Reviewed-by: Borislav Petkov <bp@alien8.de> +Acked-by: David Woodhouse <dwmw@amazon.co.uk> +Acked-by: Arjan van de Ven <arjan@linux.intel.com> +Cc: Rik van Riel <riel@redhat.com> +Cc: Andi Kleen <ak@linux.intel.com> +Cc: Paul Turner <pjt@google.com> +Cc: Peter Zijlstra <peterz@infradead.org> +Cc: Tim Chen <tim.c.chen@linux.intel.com> +Cc: Jiri Kosina <jikos@kernel.org> +Cc: Dave Hansen <dave.hansen@intel.com> +Cc: Andy Lutomirski <luto@kernel.org> +Cc: Josh Poimboeuf <jpoimboe@redhat.com> +Cc: Dan Williams <dan.j.williams@intel.com> +Cc: Linus Torvalds <torvalds@linux-foundation.org> +Cc: Greg Kroah-Hartman <gregkh@linux-foundation.org> +Cc: Kees Cook <keescook@google.com> +Link: https://lkml.kernel.org/r/20180113232730.31060.36287.stgit@tlendack-t1.amdoffice.net +Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> +--- + arch/x86/include/asm/nospec-branch.h | 6 +++++- + 1 file changed, 5 insertions(+), 1 deletion(-) + +diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h +index 402a11c..7b45d84 100644 +--- a/arch/x86/include/asm/nospec-branch.h ++++ b/arch/x86/include/asm/nospec-branch.h +@@ -11,7 +11,7 @@ + * Fill the CPU return stack buffer. + * + * Each entry in the RSB, if used for a speculative 'ret', contains an +- * infinite 'pause; jmp' loop to capture speculative execution. ++ * infinite 'pause; lfence; jmp' loop to capture speculative execution. + * + * This is required in various cases for retpoline and IBRS-based + * mitigations for the Spectre variant 2 vulnerability. Sometimes to +@@ -38,11 +38,13 @@ + call 772f; \ + 773: /* speculation trap */ \ + pause; \ ++ lfence; \ + jmp 773b; \ + 772: \ + call 774f; \ + 775: /* speculation trap */ \ + pause; \ ++ lfence; \ + jmp 775b; \ + 774: \ + dec reg; \ +@@ -73,6 +75,7 @@ + call .Ldo_rop_\@ + .Lspec_trap_\@: + pause ++ lfence + jmp .Lspec_trap_\@ + .Ldo_rop_\@: + mov \reg, (%_ASM_SP) +@@ -165,6 +168,7 @@ + " .align 16\n" \ + "901: call 903f;\n" \ + "902: pause;\n" \ ++ " lfence;\n" \ + " jmp 902b;\n" \ + " .align 16\n" \ + "903: addl $4, %%esp;\n" \ +-- +2.7.4 + |