#include <asm/cpufeatures.h>
#include <asm/msr-index.h>
#include <asm/unwind_hints.h>
+#include <asm/percpu.h>
#define RETPOLINE_THUNK_SIZE 32
.endm
/*
+ * (ab)use RETPOLINE_SAFE on RET to annotate away 'bare' RET instructions
+ * vs RETBleed validation.
+ */
+#define ANNOTATE_UNRET_SAFE ANNOTATE_RETPOLINE_SAFE
+
+/*
+ * Abuse ANNOTATE_RETPOLINE_SAFE on a NOP to indicate UNRET_END, should
+ * eventually turn into it's own annotation.
+ */
+.macro ANNOTATE_UNRET_END
+#ifdef CONFIG_DEBUG_ENTRY
+ ANNOTATE_RETPOLINE_SAFE
+ nop
+#endif
+.endm
+
+/*
+ * Equivalent to -mindirect-branch-cs-prefix; emit the 5 byte jmp/call
+ * to the retpoline thunk with a CS prefix when the register requires
+ * a RAX prefix byte to encode. Also see apply_retpolines().
+ */
+.macro __CS_PREFIX reg:req
+ .irp rs,r8,r9,r10,r11,r12,r13,r14,r15
+ .ifc \reg,\rs
+ .byte 0x2e
+ .endif
+ .endr
+.endm
+
+/*
* JMP_NOSPEC and CALL_NOSPEC macros can be used instead of a simple
* indirect jmp/call which may be susceptible to the Spectre variant 2
* attack.
*/
.macro JMP_NOSPEC reg:req
#ifdef CONFIG_RETPOLINE
- ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), \
- __stringify(jmp __x86_indirect_thunk_\reg), X86_FEATURE_RETPOLINE, \
- __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *%\reg), X86_FEATURE_RETPOLINE_LFENCE
+ __CS_PREFIX \reg
+ jmp __x86_indirect_thunk_\reg
#else
jmp *%\reg
+ int3
#endif
.endm
.macro CALL_NOSPEC reg:req
#ifdef CONFIG_RETPOLINE
- ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; call *%\reg), \
- __stringify(call __x86_indirect_thunk_\reg), X86_FEATURE_RETPOLINE, \
- __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; call *%\reg), X86_FEATURE_RETPOLINE_LFENCE
+ __CS_PREFIX \reg
+ call __x86_indirect_thunk_\reg
#else
call *%\reg
#endif
* 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_\@:
+.endm
+
+#ifdef CONFIG_CPU_UNRET_ENTRY
+#define CALL_ZEN_UNTRAIN_RET "call zen_untrain_ret"
+#else
+#define CALL_ZEN_UNTRAIN_RET ""
+#endif
+
+/*
+ * Mitigate RETBleed for AMD/Hygon Zen uarch. Requires KERNEL CR3 because the
+ * return thunk isn't mapped into the userspace tables (then again, AMD
+ * typically has NO_MELTDOWN).
+ *
+ * While zen_untrain_ret() doesn't clobber anything but requires stack,
+ * entry_ibpb() will clobber AX, CX, DX.
+ *
+ * As such, this must be placed after every *SWITCH_TO_KERNEL_CR3 at a point
+ * where we have a stack but before any RET instruction.
+ */
+.macro UNTRAIN_RET
+#if defined(CONFIG_CPU_UNRET_ENTRY) || defined(CONFIG_CPU_IBPB_ENTRY)
+ ANNOTATE_UNRET_END
+ ALTERNATIVE_2 "", \
+ CALL_ZEN_UNTRAIN_RET, X86_FEATURE_UNRET, \
+ "call entry_ibpb", X86_FEATURE_ENTRY_IBPB
#endif
.endm
_ASM_PTR " 999b\n\t" \
".popsection\n\t"
-#ifdef CONFIG_RETPOLINE
-
typedef u8 retpoline_thunk_t[RETPOLINE_THUNK_SIZE];
+extern retpoline_thunk_t __x86_indirect_thunk_array[];
+
+extern void __x86_return_thunk(void);
+extern void zen_untrain_ret(void);
+extern void entry_ibpb(void);
+
+#ifdef CONFIG_RETPOLINE
#define GEN(reg) \
extern retpoline_thunk_t __x86_indirect_thunk_ ## reg;
#include <asm/GEN-for-each-reg.h>
#undef GEN
-extern retpoline_thunk_t __x86_indirect_thunk_array[];
-
#ifdef CONFIG_X86_64
/*
SPECTRE_V2_EIBRS,
SPECTRE_V2_EIBRS_RETPOLINE,
SPECTRE_V2_EIBRS_LFENCE,
+ SPECTRE_V2_IBRS,
};
/* The indirect branch speculation control variants */
/* The Intel SPEC CTRL MSR base value cache */
extern u64 x86_spec_ctrl_base;
+DECLARE_PER_CPU(u64, x86_spec_ctrl_current);
+extern void write_spec_ctrl_current(u64 val, bool force);
+extern u64 spec_ctrl_current(void);
/*
* With retpoline, we must use IBRS to restrict branch prediction
*/
#define firmware_restrict_branch_speculation_start() \
do { \
- u64 val = x86_spec_ctrl_base | SPEC_CTRL_IBRS; \
- \
preempt_disable(); \
- alternative_msr_write(MSR_IA32_SPEC_CTRL, val, \
+ alternative_msr_write(MSR_IA32_SPEC_CTRL, \
+ spec_ctrl_current() | SPEC_CTRL_IBRS, \
X86_FEATURE_USE_IBRS_FW); \
+ alternative_msr_write(MSR_IA32_PRED_CMD, PRED_CMD_IBPB, \
+ X86_FEATURE_USE_IBPB_FW); \
} while (0)
#define firmware_restrict_branch_speculation_end() \
do { \
- u64 val = x86_spec_ctrl_base; \
- \
- alternative_msr_write(MSR_IA32_SPEC_CTRL, val, \
+ alternative_msr_write(MSR_IA32_SPEC_CTRL, \
+ spec_ctrl_current(), \
X86_FEATURE_USE_IBRS_FW); \
preempt_enable(); \
} while (0)