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kfence: use pt_regs to generate stack trace on faults 

Instead of removing the fault handling portion of the stack trace based on
the fault handler's name, just use struct pt_regs directly.

Change kfence_handle_page_fault() to take a struct pt_regs, and plumb it
through to kfence_report_error() for out-of-bounds, use-after-free, or
invalid access errors, where pt_regs is used to generate the stack trace.

If the kernel is a DEBUG_KERNEL, also show registers for more information.

Link: https://lkml.kernel.org/r/20201105092133.2075331-1-elver@google.com
Signed-off-by: Marco Elver <elver@google.com>
Suggested-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Jann Horn <jannh@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Marco Elver 2021-02-25 17:19:08 -08:00 committed by Linus Torvalds
parent 840b239863
commit d438fabce7
8 changed files with 48 additions and 46 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/arm64/include/asm/kfence.h
View File

@ -10,8 +10,6 @@
#include <asm/cacheflush.h>
#define KFENCE_SKIP_ARCH_FAULT_HANDLER "el1_sync"
static inline bool arch_kfence_init_pool(void) { return true; }
static inline bool kfence_protect_page(unsigned long addr, bool protect)

2
arch/arm64/mm/fault.c
View File

@ -390,7 +390,7 @@ static void __do_kernel_fault(unsigned long addr, unsigned int esr,
} else if (addr < PAGE_SIZE) {
msg = "NULL pointer dereference";
} else {
if (kfence_handle_page_fault(addr))
if (kfence_handle_page_fault(addr, regs))
return;
msg = "paging request";

6
arch/x86/include/asm/kfence.h
View File

@ -16,12 +16,6 @@
#include <asm/set_memory.h>
#include <asm/tlbflush.h>
/*
* The page fault handler entry function, up to which the stack trace is
* truncated in reports.
*/
#define KFENCE_SKIP_ARCH_FAULT_HANDLER "asm_exc_page_fault"
/* Force 4K pages for __kfence_pool. */
static inline bool arch_kfence_init_pool(void)
{

2
arch/x86/mm/fault.c
View File

@ -682,7 +682,7 @@ page_fault_oops(struct pt_regs *regs, unsigned long error_code,
efi_crash_gracefully_on_page_fault(address);
/* Only not-present faults should be handled by KFENCE. */
if (!(error_code & X86_PF_PROT) && kfence_handle_page_fault(address))
if (!(error_code & X86_PF_PROT) && kfence_handle_page_fault(address, regs))
return;
oops:

5
include/linux/kfence.h
View File

@ -186,6 +186,7 @@ static __always_inline __must_check bool kfence_free(void *addr)
/**
* kfence_handle_page_fault() - perform page fault handling for KFENCE pages
* @addr: faulting address
* @regs: current struct pt_regs (can be NULL, but shows full stack trace)
*
* Return:
* * false - address outside KFENCE pool,
@ -196,7 +197,7 @@ static __always_inline __must_check bool kfence_free(void *addr)
* cases KFENCE prints an error message and marks the offending page as
* present, so that the kernel can proceed.
*/
bool __must_check kfence_handle_page_fault(unsigned long addr);
bool __must_check kfence_handle_page_fault(unsigned long addr, struct pt_regs *regs);
#else /* CONFIG_KFENCE */
@ -209,7 +210,7 @@ static inline size_t kfence_ksize(const void *addr) { return 0; }
static inline void *kfence_object_start(const void *addr) { return NULL; }
static inline void __kfence_free(void *addr) { }
static inline bool __must_check kfence_free(void *addr) { return false; }
static inline bool __must_check kfence_handle_page_fault(unsigned long addr) { return false; }
static inline bool __must_check kfence_handle_page_fault(unsigned long addr, struct pt_regs *regs) { return false; }
#endif

10
mm/kfence/core.c
View File

@ -216,7 +216,7 @@ static inline bool check_canary_byte(u8 *addr)
return true;
atomic_long_inc(&counters[KFENCE_COUNTER_BUGS]);
kfence_report_error((unsigned long)addr, addr_to_metadata((unsigned long)addr),
kfence_report_error((unsigned long)addr, NULL, addr_to_metadata((unsigned long)addr),
KFENCE_ERROR_CORRUPTION);
return false;
}
@ -351,7 +351,7 @@ static void kfence_guarded_free(void *addr, struct kfence_metadata *meta, bool z
if (meta->state != KFENCE_OBJECT_ALLOCATED || meta->addr != (unsigned long)addr) {
/* Invalid or double-free, bail out. */
atomic_long_inc(&counters[KFENCE_COUNTER_BUGS]);
kfence_report_error((unsigned long)addr, meta, KFENCE_ERROR_INVALID_FREE);
kfence_report_error((unsigned long)addr, NULL, meta, KFENCE_ERROR_INVALID_FREE);
raw_spin_unlock_irqrestore(&meta->lock, flags);
return;
}
@ -766,7 +766,7 @@ void __kfence_free(void *addr)
kfence_guarded_free(addr, meta, false);
}
bool kfence_handle_page_fault(unsigned long addr)
bool kfence_handle_page_fault(unsigned long addr, struct pt_regs *regs)
{
const int page_index = (addr - (unsigned long)__kfence_pool) / PAGE_SIZE;
struct kfence_metadata *to_report = NULL;
@ -829,11 +829,11 @@ bool kfence_handle_page_fault(unsigned long addr)
out:
if (to_report) {
kfence_report_error(addr, to_report, error_type);
kfence_report_error(addr, regs, to_report, error_type);
raw_spin_unlock_irqrestore(&to_report->lock, flags);
} else {
/* This may be a UAF or OOB access, but we can't be sure. */
kfence_report_error(addr, NULL, KFENCE_ERROR_INVALID);
kfence_report_error(addr, regs, NULL, KFENCE_ERROR_INVALID);
}
return kfence_unprotect(addr); /* Unprotect and let access proceed. */

4
mm/kfence/kfence.h
View File

@ -105,8 +105,8 @@ enum kfence_error_type {
KFENCE_ERROR_INVALID_FREE, /* Invalid free. */
};
void kfence_report_error(unsigned long address, const struct kfence_metadata *meta,
enum kfence_error_type type);
void kfence_report_error(unsigned long address, struct pt_regs *regs,
const struct kfence_metadata *meta, enum kfence_error_type type);
void kfence_print_object(struct seq_file *seq, const struct kfence_metadata *meta);

63
mm/kfence/report.c
View File

@ -10,6 +10,7 @@
#include <linux/kernel.h>
#include <linux/lockdep.h>
#include <linux/printk.h>
#include <linux/sched/debug.h>
#include <linux/seq_file.h>
#include <linux/stacktrace.h>
#include <linux/string.h>
@ -41,7 +42,6 @@ static int get_stack_skipnr(const unsigned long stack_entries[], int num_entries
{
char buf[64];
int skipnr, fallback = 0;
bool is_access_fault = false;
if (type) {
/* Depending on error type, find different stack entries. */
@ -49,8 +49,12 @@ static int get_stack_skipnr(const unsigned long stack_entries[], int num_entries
case KFENCE_ERROR_UAF:
case KFENCE_ERROR_OOB:
case KFENCE_ERROR_INVALID:
is_access_fault = true;
break;
/*
* kfence_handle_page_fault() may be called with pt_regs
* set to NULL; in that case we'll simply show the full
* stack trace.
*/
return 0;
case KFENCE_ERROR_CORRUPTION:
case KFENCE_ERROR_INVALID_FREE:
break;
@ -60,26 +64,21 @@ static int get_stack_skipnr(const unsigned long stack_entries[], int num_entries
for (skipnr = 0; skipnr < num_entries; skipnr++) {
int len = scnprintf(buf, sizeof(buf), "%ps", (void *)stack_entries[skipnr]);
if (is_access_fault) {
if (!strncmp(buf, KFENCE_SKIP_ARCH_FAULT_HANDLER, len))
goto found;
} else {
if (str_has_prefix(buf, "kfence_") || str_has_prefix(buf, "__kfence_") ||
!strncmp(buf, "__slab_free", len)) {
/*
* In case of tail calls from any of the below
* to any of the above.
*/
fallback = skipnr + 1;
}
/* Also the *_bulk() variants by only checking prefixes. */
if (str_has_prefix(buf, "kfree") ||
str_has_prefix(buf, "kmem_cache_free") ||
str_has_prefix(buf, "__kmalloc") ||
str_has_prefix(buf, "kmem_cache_alloc"))
goto found;
if (str_has_prefix(buf, "kfence_") || str_has_prefix(buf, "__kfence_") ||
!strncmp(buf, "__slab_free", len)) {
/*
* In case of tail calls from any of the below
* to any of the above.
*/
fallback = skipnr + 1;
}
/* Also the *_bulk() variants by only checking prefixes. */
if (str_has_prefix(buf, "kfree") ||
str_has_prefix(buf, "kmem_cache_free") ||
str_has_prefix(buf, "__kmalloc") ||
str_has_prefix(buf, "kmem_cache_alloc"))
goto found;
}
if (fallback < num_entries)
return fallback;
@ -157,13 +156,20 @@ static void print_diff_canary(unsigned long address, size_t bytes_to_show,
pr_cont(" ]");
}
void kfence_report_error(unsigned long address, const struct kfence_metadata *meta,
enum kfence_error_type type)
void kfence_report_error(unsigned long address, struct pt_regs *regs,
const struct kfence_metadata *meta, enum kfence_error_type type)
{
unsigned long stack_entries[KFENCE_STACK_DEPTH] = { 0 };
int num_stack_entries = stack_trace_save(stack_entries, KFENCE_STACK_DEPTH, 1);
int skipnr = get_stack_skipnr(stack_entries, num_stack_entries, &type);
const ptrdiff_t object_index = meta ? meta - kfence_metadata : -1;
int num_stack_entries;
int skipnr = 0;
if (regs) {
num_stack_entries = stack_trace_save_regs(regs, stack_entries, KFENCE_STACK_DEPTH, 0);
} else {
num_stack_entries = stack_trace_save(stack_entries, KFENCE_STACK_DEPTH, 1);
skipnr = get_stack_skipnr(stack_entries, num_stack_entries, &type);
}
/* Require non-NULL meta, except if KFENCE_ERROR_INVALID. */
if (WARN_ON(type != KFENCE_ERROR_INVALID && !meta))
@ -227,7 +233,10 @@ void kfence_report_error(unsigned long address, const struct kfence_metadata *me
/* Print report footer. */
pr_err("\n");
dump_stack_print_info(KERN_ERR);
if (IS_ENABLED(CONFIG_DEBUG_KERNEL) && regs)
show_regs(regs);
else
dump_stack_print_info(KERN_ERR);
pr_err("==================================================================\n");
lockdep_on();