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Subject[PATCH 39/43] x86: kmsan: handle register passing from uninstrumented code
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When calling KMSAN-instrumented functions from non-instrumented
functions, function parameters may not be initialized properly, leading
to false positive reports. In particular, this happens all the time when
calling interrupt handlers from `noinstr` IDT entries.

Fortunately, x86 code has instrumentation_begin() and
instrumentation_end(), which denote the regions where `noinstr` code
calls potentially instrumented code. We add calls to
kmsan_instrumentation_begin() to those regions, which:
- wipe the current KMSAN state at the beginning of the region, ensuring
that the first call of an instrumented function receives initialized
parameters (this is a pretty good approximation of having all other
instrumented functions receive initialized parameters);
- unpoison the `struct pt_regs` set up by the non-instrumented assembly
code.

Signed-off-by: Alexander Potapenko <glider@google.com>
---
Link: https://linux-review.googlesource.com/id/I435ec076cd21752c2f877f5da81f5eced62a2ea4
---
arch/x86/entry/common.c | 2 ++
arch/x86/include/asm/idtentry.h | 5 +++++
arch/x86/kernel/cpu/mce/core.c | 1 +
arch/x86/kernel/kvm.c | 1 +
arch/x86/kernel/nmi.c | 1 +
arch/x86/kernel/sev.c | 2 ++
arch/x86/kernel/traps.c | 7 +++++++
arch/x86/mm/fault.c | 1 +
kernel/entry/common.c | 3 +++
9 files changed, 23 insertions(+)

diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index 6c2826417b337..a0f90588c514e 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -14,6 +14,7 @@
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/errno.h>
+#include <linux/kmsan.h>
#include <linux/ptrace.h>
#include <linux/export.h>
#include <linux/nospec.h>
@@ -76,6 +77,7 @@ __visible noinstr void do_syscall_64(struct pt_regs *regs, int nr)
nr = syscall_enter_from_user_mode(regs, nr);

instrumentation_begin();
+ kmsan_instrumentation_begin(regs);

if (!do_syscall_x64(regs, nr) && !do_syscall_x32(regs, nr) && nr != -1) {
/* Invalid system call, but still a system call. */
diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
index 1345088e99025..f025fdc0f25df 100644
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@@ -52,6 +52,7 @@ __visible noinstr void func(struct pt_regs *regs) \
irqentry_state_t state = irqentry_enter(regs); \
\
instrumentation_begin(); \
+ kmsan_instrumentation_begin(regs); \
__##func (regs); \
instrumentation_end(); \
irqentry_exit(regs, state); \
@@ -99,6 +100,7 @@ __visible noinstr void func(struct pt_regs *regs, \
irqentry_state_t state = irqentry_enter(regs); \
\
instrumentation_begin(); \
+ kmsan_instrumentation_begin(regs); \
__##func (regs, error_code); \
instrumentation_end(); \
irqentry_exit(regs, state); \
@@ -196,6 +198,7 @@ __visible noinstr void func(struct pt_regs *regs, \
u32 vector = (u32)(u8)error_code; \
\
instrumentation_begin(); \
+ kmsan_instrumentation_begin(regs); \
kvm_set_cpu_l1tf_flush_l1d(); \
run_irq_on_irqstack_cond(__##func, regs, vector); \
instrumentation_end(); \
@@ -236,6 +239,7 @@ __visible noinstr void func(struct pt_regs *regs) \
irqentry_state_t state = irqentry_enter(regs); \
\
instrumentation_begin(); \
+ kmsan_instrumentation_begin(regs); \
kvm_set_cpu_l1tf_flush_l1d(); \
run_sysvec_on_irqstack_cond(__##func, regs); \
instrumentation_end(); \
@@ -263,6 +267,7 @@ __visible noinstr void func(struct pt_regs *regs) \
irqentry_state_t state = irqentry_enter(regs); \
\
instrumentation_begin(); \
+ kmsan_instrumentation_begin(regs); \
__irq_enter_raw(); \
kvm_set_cpu_l1tf_flush_l1d(); \
__##func (regs); \
diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
index 6ed365337a3b1..b49e2c6bb8ca2 100644
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -1314,6 +1314,7 @@ static void queue_task_work(struct mce *m, char *msg, void (*func)(struct callba
static noinstr void unexpected_machine_check(struct pt_regs *regs)
{
instrumentation_begin();
+ kmsan_instrumentation_begin(regs);
pr_err("CPU#%d: Unexpected int18 (Machine Check)\n",
smp_processor_id());
instrumentation_end();
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 59abbdad7729c..55ffe1bc73b00 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -250,6 +250,7 @@ noinstr bool __kvm_handle_async_pf(struct pt_regs *regs, u32 token)

state = irqentry_enter(regs);
instrumentation_begin();
+ kmsan_instrumentation_begin(regs);

/*
* If the host managed to inject an async #PF into an interrupt
diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
index 4bce802d25fb1..d91327d271359 100644
--- a/arch/x86/kernel/nmi.c
+++ b/arch/x86/kernel/nmi.c
@@ -330,6 +330,7 @@ static noinstr void default_do_nmi(struct pt_regs *regs)
__this_cpu_write(last_nmi_rip, regs->ip);

instrumentation_begin();
+ kmsan_instrumentation_begin(regs);

handled = nmi_handle(NMI_LOCAL, regs);
__this_cpu_add(nmi_stats.normal, handled);
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index a9fc2ac7a8bd5..421d59b982cae 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -1426,6 +1426,7 @@ DEFINE_IDTENTRY_VC_KERNEL(exc_vmm_communication)
irq_state = irqentry_nmi_enter(regs);

instrumentation_begin();
+ kmsan_instrumentation_begin(regs);

if (!vc_raw_handle_exception(regs, error_code)) {
/* Show some debug info */
@@ -1458,6 +1459,7 @@ DEFINE_IDTENTRY_VC_USER(exc_vmm_communication)

irqentry_enter_from_user_mode(regs);
instrumentation_begin();
+ kmsan_instrumentation_begin(regs);

if (!vc_raw_handle_exception(regs, error_code)) {
/*
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index c9d566dcf89a0..3a821010def63 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -230,6 +230,7 @@ static noinstr bool handle_bug(struct pt_regs *regs)
* All lies, just get the WARN/BUG out.
*/
instrumentation_begin();
+ kmsan_instrumentation_begin(regs);
/*
* Since we're emulating a CALL with exceptions, restore the interrupt
* state to what it was at the exception site.
@@ -261,6 +262,7 @@ DEFINE_IDTENTRY_RAW(exc_invalid_op)

state = irqentry_enter(regs);
instrumentation_begin();
+ kmsan_instrumentation_begin(regs);
handle_invalid_op(regs);
instrumentation_end();
irqentry_exit(regs, state);
@@ -415,6 +417,7 @@ DEFINE_IDTENTRY_DF(exc_double_fault)

irqentry_nmi_enter(regs);
instrumentation_begin();
+ kmsan_instrumentation_begin(regs);
notify_die(DIE_TRAP, str, regs, error_code, X86_TRAP_DF, SIGSEGV);

tsk->thread.error_code = error_code;
@@ -690,6 +693,7 @@ DEFINE_IDTENTRY_RAW(exc_int3)
if (user_mode(regs)) {
irqentry_enter_from_user_mode(regs);
instrumentation_begin();
+ kmsan_instrumentation_begin(regs);
do_int3_user(regs);
instrumentation_end();
irqentry_exit_to_user_mode(regs);
@@ -697,6 +701,7 @@ DEFINE_IDTENTRY_RAW(exc_int3)
irqentry_state_t irq_state = irqentry_nmi_enter(regs);

instrumentation_begin();
+ kmsan_instrumentation_begin(regs);
if (!do_int3(regs))
die("int3", regs, 0);
instrumentation_end();
@@ -896,6 +901,7 @@ static __always_inline void exc_debug_kernel(struct pt_regs *regs,
unsigned long dr7 = local_db_save();
irqentry_state_t irq_state = irqentry_nmi_enter(regs);
instrumentation_begin();
+ kmsan_instrumentation_begin(regs);

/*
* If something gets miswired and we end up here for a user mode
@@ -975,6 +981,7 @@ static __always_inline void exc_debug_user(struct pt_regs *regs,

irqentry_enter_from_user_mode(regs);
instrumentation_begin();
+ kmsan_instrumentation_begin(regs);

/*
* Start the virtual/ptrace DR6 value with just the DR_STEP mask
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index abed0aedf00d2..0437d2fe31ecb 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1558,6 +1558,7 @@ DEFINE_IDTENTRY_RAW_ERRORCODE(exc_page_fault)
state = irqentry_enter(regs);

instrumentation_begin();
+ kmsan_instrumentation_begin(regs);
handle_page_fault(regs, error_code, address);
instrumentation_end();

diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index d5a61d565ad5d..3a569ea5a78fb 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -104,6 +104,7 @@ noinstr long syscall_enter_from_user_mode(struct pt_regs *regs, long syscall)
__enter_from_user_mode(regs);

instrumentation_begin();
+ kmsan_instrumentation_begin(regs);
local_irq_enable();
ret = __syscall_enter_from_user_work(regs, syscall);
instrumentation_end();
@@ -297,6 +298,7 @@ void syscall_exit_to_user_mode_work(struct pt_regs *regs)
__visible noinstr void syscall_exit_to_user_mode(struct pt_regs *regs)
{
instrumentation_begin();
+ kmsan_instrumentation_begin(regs);
__syscall_exit_to_user_mode_work(regs);
instrumentation_end();
__exit_to_user_mode();
@@ -310,6 +312,7 @@ noinstr void irqentry_enter_from_user_mode(struct pt_regs *regs)
noinstr void irqentry_exit_to_user_mode(struct pt_regs *regs)
{
instrumentation_begin();
+ kmsan_instrumentation_begin(regs);
exit_to_user_mode_prepare(regs);
instrumentation_end();
__exit_to_user_mode();
--
2.34.1.173.g76aa8bc2d0-goog
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