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Subject[tip: x86/entry] x86/entry: Fixup bad_iret vs noinstr
The following commit has been merged into the x86/entry branch of tip:

Commit-ID: e3a9e681adb779b39565a28b3252c3be1033f994
Gitweb: https://git.kernel.org/tip/e3a9e681adb779b39565a28b3252c3be1033f994
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Wed, 17 Jun 2020 18:21:16 +02:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Thu, 25 Jun 2020 13:45:39 +02:00

x86/entry: Fixup bad_iret vs noinstr

vmlinux.o: warning: objtool: fixup_bad_iret()+0x8e: call to memcpy() leaves .noinstr.text section

Worse, when KASAN there is no telling what memcpy() actually is. Force
the use of __memcpy() which is our assmebly implementation.

Reported-by: Marco Elver <elver@google.com>
Suggested-by: Marco Elver <elver@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Marco Elver <elver@google.com>
Link: https://lkml.kernel.org/r/20200618144801.760070502@infradead.org
---
arch/x86/kernel/traps.c | 6 +++---
arch/x86/lib/memcpy_64.S | 4 ++++
2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index af75109..a7d1570 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -690,13 +690,13 @@ struct bad_iret_stack *fixup_bad_iret(struct bad_iret_stack *s)
(struct bad_iret_stack *)__this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;

/* Copy the IRET target to the temporary storage. */
- memcpy(&tmp.regs.ip, (void *)s->regs.sp, 5*8);
+ __memcpy(&tmp.regs.ip, (void *)s->regs.sp, 5*8);

/* Copy the remainder of the stack from the current stack. */
- memcpy(&tmp, s, offsetof(struct bad_iret_stack, regs.ip));
+ __memcpy(&tmp, s, offsetof(struct bad_iret_stack, regs.ip));

/* Update the entry stack */
- memcpy(new_stack, &tmp, sizeof(tmp));
+ __memcpy(new_stack, &tmp, sizeof(tmp));

BUG_ON(!user_mode(&new_stack->regs));
return new_stack;
diff --git a/arch/x86/lib/memcpy_64.S b/arch/x86/lib/memcpy_64.S
index 56b243b..bbcc05b 100644
--- a/arch/x86/lib/memcpy_64.S
+++ b/arch/x86/lib/memcpy_64.S
@@ -8,6 +8,8 @@
#include <asm/alternative-asm.h>
#include <asm/export.h>

+.pushsection .noinstr.text, "ax"
+
/*
* We build a jump to memcpy_orig by default which gets NOPped out on
* the majority of x86 CPUs which set REP_GOOD. In addition, CPUs which
@@ -184,6 +186,8 @@ SYM_FUNC_START_LOCAL(memcpy_orig)
retq
SYM_FUNC_END(memcpy_orig)

+.popsection
+
#ifndef CONFIG_UML

MCSAFE_TEST_CTL
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