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x86/retpoline: Ensure default return thunk isn't used at runtime 

Make sure the default return thunk is not used after all return
instructions have been patched by the alternatives because the default
return thunk is insufficient when it comes to mitigating Retbleed or
SRSO.

Fix based on an earlier version by David Kaplan <david.kaplan@amd.com>.

  [ bp: Fix the compilation error of warn_thunk_thunk being an invisible
        symbol, hoist thunk macro into calling.h ]

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Co-developed-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20231010171020.462211-4-david.kaplan@amd.com
Link: https://lore.kernel.org/r/20240104132446.GEZZaxnrIgIyat0pqf@fat_crate.local
This commit is contained in:
Josh Poimboeuf 2024-01-03 19:36:26 +01:00 committed by Borislav Petkov (AMD)
parent 0911b8c52c
commit 4461438a84
7 changed files with 85 additions and 68 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

60
arch/x86/entry/calling.h
View File

@ -426,3 +426,63 @@ For 32-bit we have the following conventions - kernel is built with
.endm
#endif /* CONFIG_SMP */
#ifdef CONFIG_X86_64
/* rdi: arg1 ... normal C conventions. rax is saved/restored. */
.macro THUNK name, func
SYM_FUNC_START(\name)
pushq %rbp
movq %rsp, %rbp
pushq %rdi
pushq %rsi
pushq %rdx
pushq %rcx
pushq %rax
pushq %r8
pushq %r9
pushq %r10
pushq %r11
call \func
popq %r11
popq %r10
popq %r9
popq %r8
popq %rax
popq %rcx
popq %rdx
popq %rsi
popq %rdi
popq %rbp
RET
SYM_FUNC_END(\name)
_ASM_NOKPROBE(\name)
.endm
#else /* CONFIG_X86_32 */
/* put return address in eax (arg1) */
.macro THUNK name, func, put_ret_addr_in_eax=0
SYM_CODE_START_NOALIGN(\name)
pushl %eax
pushl %ecx
pushl %edx
.if \put_ret_addr_in_eax
/* Place EIP in the arg1 */
movl 3*4(%esp), %eax
.endif
call \func
popl %edx
popl %ecx
popl %eax
RET
_ASM_NOKPROBE(\name)
SYM_CODE_END(\name)
.endm
#endif

4
arch/x86/entry/entry.S
View File

@ -7,6 +7,8 @@
#include <linux/linkage.h>
#include <asm/msr-index.h>
#include "calling.h"
.pushsection .noinstr.text, "ax"
SYM_FUNC_START(entry_ibpb)
@ -20,3 +22,5 @@ SYM_FUNC_END(entry_ibpb)
EXPORT_SYMBOL_GPL(entry_ibpb);
.popsection
THUNK warn_thunk_thunk, __warn_thunk

34
arch/x86/entry/thunk_32.S
View File

@ -4,33 +4,15 @@
* Copyright 2008 by Steven Rostedt, Red Hat, Inc
* (inspired by Andi Kleen's thunk_64.S)
*/
#include <linux/export.h>
#include <linux/linkage.h>
#include <asm/asm.h>
/* put return address in eax (arg1) */
.macro THUNK name, func, put_ret_addr_in_eax=0
SYM_CODE_START_NOALIGN(\name)
pushl %eax
pushl %ecx
pushl %edx
#include <linux/export.h>
#include <linux/linkage.h>
#include <asm/asm.h>
.if \put_ret_addr_in_eax
/* Place EIP in the arg1 */
movl 3*4(%esp), %eax
.endif
#include "calling.h"
call \func
popl %edx
popl %ecx
popl %eax
RET
_ASM_NOKPROBE(\name)
SYM_CODE_END(\name)
.endm
THUNK preempt_schedule_thunk, preempt_schedule
THUNK preempt_schedule_notrace_thunk, preempt_schedule_notrace
EXPORT_SYMBOL(preempt_schedule_thunk)
EXPORT_SYMBOL(preempt_schedule_notrace_thunk)
THUNK preempt_schedule_thunk, preempt_schedule
THUNK preempt_schedule_notrace_thunk, preempt_schedule_notrace
EXPORT_SYMBOL(preempt_schedule_thunk)
EXPORT_SYMBOL(preempt_schedule_notrace_thunk)

33
arch/x86/entry/thunk_64.S
View File

@ -9,39 +9,6 @@
#include "calling.h"
#include <asm/asm.h>
/* rdi: arg1 ... normal C conventions. rax is saved/restored. */
.macro THUNK name, func
SYM_FUNC_START(\name)
pushq %rbp
movq %rsp, %rbp
pushq %rdi
pushq %rsi
pushq %rdx
pushq %rcx
pushq %rax
pushq %r8
pushq %r9
pushq %r10
pushq %r11
call \func
popq %r11
popq %r10
popq %r9
popq %r8
popq %rax
popq %rcx
popq %rdx
popq %rsi
popq %rdi
popq %rbp
RET
SYM_FUNC_END(\name)
_ASM_NOKPROBE(\name)
.endm
THUNK preempt_schedule_thunk, preempt_schedule
THUNK preempt_schedule_notrace_thunk, preempt_schedule_notrace
EXPORT_SYMBOL(preempt_schedule_thunk)

2
arch/x86/include/asm/nospec-branch.h
View File

@ -357,6 +357,8 @@ extern void entry_ibpb(void);
extern void (*x86_return_thunk)(void);
extern void __warn_thunk(void);
#ifdef CONFIG_MITIGATION_CALL_DEPTH_TRACKING
extern void call_depth_return_thunk(void);

5
arch/x86/kernel/cpu/bugs.c
View File

@ -2850,3 +2850,8 @@ ssize_t cpu_show_gds(struct device *dev, struct device_attribute *attr, char *bu
return cpu_show_common(dev, attr, buf, X86_BUG_GDS);
}
#endif
void __warn_thunk(void)
{
WARN_ONCE(1, "Unpatched return thunk in use. This should not happen!\n");
}

15
arch/x86/lib/retpoline.S
View File

@ -369,19 +369,16 @@ SYM_FUNC_END(call_depth_return_thunk)
* 'JMP __x86_return_thunk' sites are changed to something else by
* apply_returns().
*
* This should be converted eventually to call a warning function which
* should scream loudly when the default return thunk is called after
* alternatives have been applied.
*
* That warning function cannot BUG() because the bug splat cannot be
* displayed in all possible configurations, leading to users not really
* knowing why the machine froze.
* The ALTERNATIVE below adds a really loud warning to catch the case
* where the insufficient default return thunk ends up getting used for
* whatever reason like miscompilation or failure of
* objtool/alternatives/etc to patch all the return sites.
*/
SYM_CODE_START(__x86_return_thunk)
UNWIND_HINT_FUNC
ANNOTATE_NOENDBR
ANNOTATE_UNRET_SAFE
ret
ALTERNATIVE __stringify(ANNOTATE_UNRET_SAFE; ret), \
"jmp warn_thunk_thunk", X86_FEATURE_ALWAYS
int3
SYM_CODE_END(__x86_return_thunk)
EXPORT_SYMBOL(__x86_return_thunk)