Commit 42be649d authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Borislav Petkov (AMD)
Browse files

x86/cpu: Rename srso_(.*)_alias to srso_alias_\1 



For a more consistent namespace.

  [ bp: Fixup names in the doc too. ]

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarBorislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230814121148.976236447@infradead.org
parent d025b7ba

Documentation/admin-guide/hw-vuln/srso.rst

+2 −2
Original line number Diff line number Diff line
@@ -141,8 +141,8 @@ sequence. 
To ensure the safety of this mitigation, the kernel must ensure that the

safe return sequence is itself free from attacker interference.  In Zen3

and Zen4, this is accomplished by creating a BTB alias between the

untraining function srso_untrain_ret_alias() and the safe return

function srso_safe_ret_alias() which results in evicting a potentially

untraining function srso_alias_untrain_ret() and the safe return

function srso_alias_safe_ret() which results in evicting a potentially

poisoned BTB entry and using that safe one for all function returns.



In older Zen1 and Zen2, this is accomplished using a reinterpretation

arch/x86/include/asm/nospec-branch.h

+3 −3
Original line number Diff line number Diff line
@@ -300,7 +300,7 @@ 


#ifdef CONFIG_CPU_SRSO

	ALTERNATIVE_2 "", "call srso_untrain_ret", X86_FEATURE_SRSO, \

			  "call srso_untrain_ret_alias", X86_FEATURE_SRSO_ALIAS

			  "call srso_alias_untrain_ret", X86_FEATURE_SRSO_ALIAS

#endif

.endm
@@ -316,7 +316,7 @@ 


#ifdef CONFIG_CPU_SRSO

	ALTERNATIVE_2 "", "call srso_untrain_ret", X86_FEATURE_SRSO, \

			  "call srso_untrain_ret_alias", X86_FEATURE_SRSO_ALIAS

			  "call srso_alias_untrain_ret", X86_FEATURE_SRSO_ALIAS

#endif

.endm
@@ -353,7 +353,7 @@ extern void srso_alias_return_thunk(void); 


extern void retbleed_untrain_ret(void);

extern void srso_untrain_ret(void);

extern void srso_untrain_ret_alias(void);

extern void srso_alias_untrain_ret(void);



extern void entry_ibpb(void);

arch/x86/kernel/vmlinux.lds.S

+4 −4
Original line number Diff line number Diff line
@@ -147,10 +147,10 @@ SECTIONS 


#ifdef CONFIG_CPU_SRSO

		/*

		 * See the comment above srso_untrain_ret_alias()'s

		 * See the comment above srso_alias_untrain_ret()'s

		 * definition.

		 */

		. = srso_untrain_ret_alias | (1 << 2) | (1 << 8) | (1 << 14) | (1 << 20);

		. = srso_alias_untrain_ret | (1 << 2) | (1 << 8) | (1 << 14) | (1 << 20);

		*(.text..__x86.rethunk_safe)

#endif

		ALIGN_ENTRY_TEXT_END
@@ -536,8 +536,8 @@ INIT_PER_CPU(irq_stack_backing_store); 
 * Instead do: (A | B) - (A & B) in order to compute the XOR

 * of the two function addresses:

 */

. = ASSERT(((ABSOLUTE(srso_untrain_ret_alias) | srso_safe_ret_alias) -

		(ABSOLUTE(srso_untrain_ret_alias) & srso_safe_ret_alias)) == ((1 << 2) | (1 << 8) | (1 << 14) | (1 << 20)),

. = ASSERT(((ABSOLUTE(srso_alias_untrain_ret) | srso_alias_safe_ret) -

		(ABSOLUTE(srso_alias_untrain_ret) & srso_alias_safe_ret)) == ((1 << 2) | (1 << 8) | (1 << 14) | (1 << 20)),

		"SRSO function pair won't alias");

#endif

arch/x86/lib/retpoline.S

+13 −13
Original line number Diff line number Diff line
@@ -133,56 +133,56 @@ SYM_CODE_END(__x86_indirect_jump_thunk_array) 
#ifdef CONFIG_RETHUNK



/*

 * srso_untrain_ret_alias() and srso_safe_ret_alias() are placed at

 * srso_alias_untrain_ret() and srso_alias_safe_ret() are placed at

 * special addresses:

 *

 * - srso_untrain_ret_alias() is 2M aligned

 * - srso_safe_ret_alias() is also in the same 2M page but bits 2, 8, 14

 * - srso_alias_untrain_ret() is 2M aligned

 * - srso_alias_safe_ret() is also in the same 2M page but bits 2, 8, 14

 * and 20 in its virtual address are set (while those bits in the

 * srso_untrain_ret_alias() function are cleared).

 * srso_alias_untrain_ret() function are cleared).

 *

 * This guarantees that those two addresses will alias in the branch

 * target buffer of Zen3/4 generations, leading to any potential

 * poisoned entries at that BTB slot to get evicted.

 *

 * As a result, srso_safe_ret_alias() becomes a safe return.

 * As a result, srso_alias_safe_ret() becomes a safe return.

 */

#ifdef CONFIG_CPU_SRSO

	.section .text..__x86.rethunk_untrain



SYM_START(srso_untrain_ret_alias, SYM_L_GLOBAL, SYM_A_NONE)

SYM_START(srso_alias_untrain_ret, SYM_L_GLOBAL, SYM_A_NONE)

	UNWIND_HINT_FUNC

	ANNOTATE_NOENDBR

	ASM_NOP2

	lfence

	jmp srso_alias_return_thunk

SYM_FUNC_END(srso_untrain_ret_alias)

__EXPORT_THUNK(srso_untrain_ret_alias)

SYM_FUNC_END(srso_alias_untrain_ret)

__EXPORT_THUNK(srso_alias_untrain_ret)



	.section .text..__x86.rethunk_safe

#else

/* dummy definition for alternatives */

SYM_START(srso_untrain_ret_alias, SYM_L_GLOBAL, SYM_A_NONE)

SYM_START(srso_alias_untrain_ret, SYM_L_GLOBAL, SYM_A_NONE)

	ANNOTATE_UNRET_SAFE

	ret

	int3

SYM_FUNC_END(srso_untrain_ret_alias)

SYM_FUNC_END(srso_alias_untrain_ret)

#endif



SYM_START(srso_safe_ret_alias, SYM_L_GLOBAL, SYM_A_NONE)

SYM_START(srso_alias_safe_ret, SYM_L_GLOBAL, SYM_A_NONE)

	lea 8(%_ASM_SP), %_ASM_SP

	UNWIND_HINT_FUNC

	ANNOTATE_UNRET_SAFE

	ret

	int3

SYM_FUNC_END(srso_safe_ret_alias)

SYM_FUNC_END(srso_alias_safe_ret)



	.section .text..__x86.return_thunk



SYM_CODE_START(srso_alias_return_thunk)

	UNWIND_HINT_FUNC

	ANNOTATE_NOENDBR

	call srso_safe_ret_alias

	call srso_alias_safe_ret

	ud2

SYM_CODE_END(srso_alias_return_thunk)