[PATCH 5.15 59/89] x86/speculation: Fix RSB filling with CONFIG_RETPOLINE=n

Greg Kroah-Hartman
2022-07-22T09:27:07Z

From: Josh Poimboeuf <jpoimboe@kernel.org>

commit b2620facef4889fefcbf2e87284f34dcd4189bce upstream.

If a kernel is built with CONFIG_RETPOLINE=n, but the user still wants
to mitigate Spectre v2 using IBRS or eIBRS, the RSB filling will be
silently disabled.

There's nothing retpoline-specific about RSB buffer filling. Remove the
CONFIG_RETPOLINE guards around it.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/entry/entry_32.S | 2 --
arch/x86/entry/entry_64.S | 2 --
arch/x86/include/asm/nospec-branch.h | 2 --
3 files changed, 6 deletions(-)

--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -701,7 +701,6 @@ SYM_CODE_START(__switch_to_asm)
movl %ebx, PER_CPU_VAR(__stack_chk_guard)
#endif

-#ifdef CONFIG_RETPOLINE
/*
* When switching from a shallower to a deeper call stack
* the RSB may either underflow or use entries populated
@@ -710,7 +709,6 @@ SYM_CODE_START(__switch_to_asm)
* speculative execution to prevent attack.
*/
FILL_RETURN_BUFFER %ebx, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_CTXSW
-#endif

/* Restore flags or the incoming task to restore AC state. */
popfl
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -248,7 +248,6 @@ SYM_FUNC_START(__switch_to_asm)
movq %rbx, PER_CPU_VAR(fixed_percpu_data) + stack_canary_offset
#endif

-#ifdef CONFIG_RETPOLINE
/*
* When switching from a shallower to a deeper call stack
* the RSB may either underflow or use entries populated
@@ -257,7 +256,6 @@ SYM_FUNC_START(__switch_to_asm)
* speculative execution to prevent attack.
*/
FILL_RETURN_BUFFER %r12, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_CTXSW
-#endif

/* restore callee-saved registers */
popq %r15
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -122,11 +122,9 @@
* monstrosity above, manually.
*/
.macro FILL_RETURN_BUFFER reg:req nr:req ftr:req
-#ifdef CONFIG_RETPOLINE
ALTERNATIVE "jmp .Lskip_rsb_\@", "", \ftr
__FILL_RETURN_BUFFER(\reg,\nr,%_ASM_SP)
.Lskip_rsb_\@:
-#endif
.endm

/*