[PATCH 5.4 19/51] x86/speculation: Fix RSB filling with CONFIG_RETPOLINE=n

From: Greg Kroah-Hartman
Date: Wed Oct 05 2022 - 07:39:06 EST


From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>

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@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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
@@ -750,7 +750,6 @@ ENTRY(__switch_to_asm)
movl %ebx, PER_CPU_VAR(stack_canary)+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
@@ -759,7 +758,6 @@ ENTRY(__switch_to_asm)
* speculative execution to prevent attack.
*/
FILL_RETURN_BUFFER %ebx, RSB_CLEAR_LOOPS, X86_FEATURE_RSB_CTXSW
-#endif

/* restore callee-saved registers */
popfl
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -305,7 +305,6 @@ ENTRY(__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
@@ -314,7 +313,6 @@ ENTRY(__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
@@ -155,11 +155,9 @@
* 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

#else /* __ASSEMBLY__ */