The patch titled
Subject: kfence: report sensitive information based on no_hash_pointers
has been added to the -mm tree. Its filename is
kfence-report-sensitive-information-based-on-no_hash_pointers.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/kfence-report-sensitive-information-based-on-no_hash_pointers.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/kfence-report-sensitive-information-based-on-no_hash_pointers.patch
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Marco Elver <elver@xxxxxxxxxx>
Subject: kfence: report sensitive information based on no_hash_pointers
We cannot rely on CONFIG_DEBUG_KERNEL to decide if we're running a "debug
kernel" where we can safely show potentially sensitive information in the
kernel log.
Instead, simply rely on the newly introduced "no_hash_pointers" to print
unhashed kernel pointers, as well as decide if our reports can include
other potentially sensitive information such as registers and corrupted
bytes.
Link: https://lkml.kernel.org/r/20210223082043.1972742-1-elver@xxxxxxxxxx
Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
Cc: Timur Tabi <timur@xxxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/dev-tools/kfence.rst | 8 ++++----
mm/kfence/core.c | 10 +++-------
mm/kfence/kfence.h | 7 -------
mm/kfence/kfence_test.c | 2 +-
mm/kfence/report.c | 18 ++++++++++--------
5 files changed, 18 insertions(+), 27 deletions(-)
--- a/Documentation/dev-tools/kfence.rst~kfence-report-sensitive-information-based-on-no_hash_pointers
+++ a/Documentation/dev-tools/kfence.rst
@@ -88,8 +88,8 @@ A typical out-of-bounds access looks lik
The header of the report provides a short summary of the function involved in
the access. It is followed by more detailed information about the access and
-its origin. Note that, real kernel addresses are only shown for
-``CONFIG_DEBUG_KERNEL=y`` builds.
+its origin. Note that, real kernel addresses are only shown when using the
+kernel command line option ``no_hash_pointers``.
Use-after-free accesses are reported as::
@@ -184,8 +184,8 @@ invalidly written bytes (offset from the
representation, '.' denote untouched bytes. In the example above ``0xac`` is
the value written to the invalid address at offset 0, and the remaining '.'
denote that no following bytes have been touched. Note that, real values are
-only shown for ``CONFIG_DEBUG_KERNEL=y`` builds; to avoid information
-disclosure for non-debug builds, '!' is used instead to denote invalidly
+only shown if the kernel was booted with ``no_hash_pointers``; to avoid
+information disclosure otherwise, '!' is used instead to denote invalidly
written bytes.
And finally, KFENCE may also report on invalid accesses to any protected page
--- a/mm/kfence/core.c~kfence-report-sensitive-information-based-on-no_hash_pointers
+++ a/mm/kfence/core.c
@@ -646,13 +646,9 @@ void __init kfence_init(void)
WRITE_ONCE(kfence_enabled, true);
schedule_delayed_work(&kfence_timer, 0);
- pr_info("initialized - using %lu bytes for %d objects", KFENCE_POOL_SIZE,
- CONFIG_KFENCE_NUM_OBJECTS);
- if (IS_ENABLED(CONFIG_DEBUG_KERNEL))
- pr_cont(" at 0x%px-0x%px\n", (void *)__kfence_pool,
- (void *)(__kfence_pool + KFENCE_POOL_SIZE));
- else
- pr_cont("\n");
+ pr_info("initialized - using %lu bytes for %d objects at 0x%p-0x%p\n", KFENCE_POOL_SIZE,
+ CONFIG_KFENCE_NUM_OBJECTS, (void *)__kfence_pool,
+ (void *)(__kfence_pool + KFENCE_POOL_SIZE));
}
void kfence_shutdown_cache(struct kmem_cache *s)
--- a/mm/kfence/kfence.h~kfence-report-sensitive-information-based-on-no_hash_pointers
+++ a/mm/kfence/kfence.h
@@ -16,13 +16,6 @@
#include "../slab.h" /* for struct kmem_cache */
-/* For non-debug builds, avoid leaking kernel pointers into dmesg. */
-#ifdef CONFIG_DEBUG_KERNEL
-#define PTR_FMT "%px"
-#else
-#define PTR_FMT "%p"
-#endif
-
/*
* Get the canary byte pattern for @addr. Use a pattern that varies based on the
* lower 3 bits of the address, to detect memory corruptions with higher
--- a/mm/kfence/kfence_test.c~kfence-report-sensitive-information-based-on-no_hash_pointers
+++ a/mm/kfence/kfence_test.c
@@ -146,7 +146,7 @@ static bool report_matches(const struct
break;
}
- cur += scnprintf(cur, end - cur, " 0x" PTR_FMT, (void *)r->addr);
+ cur += scnprintf(cur, end - cur, " 0x%p", (void *)r->addr);
spin_lock_irqsave(&observed.lock, flags);
if (!report_available())
--- a/mm/kfence/report.c~kfence-report-sensitive-information-based-on-no_hash_pointers
+++ a/mm/kfence/report.c
@@ -19,6 +19,8 @@
#include "kfence.h"
+extern bool no_hash_pointers;
+
/* Helper function to either print to a seq_file or to console. */
__printf(2, 3)
static void seq_con_printf(struct seq_file *seq, const char *fmt, ...)
@@ -118,7 +120,7 @@ void kfence_print_object(struct seq_file
}
seq_con_printf(seq,
- "kfence-#%zd [0x" PTR_FMT "-0x" PTR_FMT
+ "kfence-#%zd [0x%p-0x%p"
", size=%d, cache=%s] allocated by task %d:\n",
meta - kfence_metadata, (void *)start, (void *)(start + size - 1), size,
(cache && cache->name) ? cache->name : "<destroyed>", meta->alloc_track.pid);
@@ -148,7 +150,7 @@ static void print_diff_canary(unsigned l
for (cur = (const u8 *)address; cur < end; cur++) {
if (*cur == KFENCE_CANARY_PATTERN(cur))
pr_cont(" .");
- else if (IS_ENABLED(CONFIG_DEBUG_KERNEL))
+ else if (no_hash_pointers)
pr_cont(" 0x%02x", *cur);
else /* Do not leak kernel memory in non-debug builds. */
pr_cont(" !");
@@ -201,7 +203,7 @@ void kfence_report_error(unsigned long a
pr_err("BUG: KFENCE: out-of-bounds %s in %pS\n\n", get_access_type(is_write),
(void *)stack_entries[skipnr]);
- pr_err("Out-of-bounds %s at 0x" PTR_FMT " (%luB %s of kfence-#%zd):\n",
+ pr_err("Out-of-bounds %s at 0x%p (%luB %s of kfence-#%zd):\n",
get_access_type(is_write), (void *)address,
left_of_object ? meta->addr - address : address - meta->addr,
left_of_object ? "left" : "right", object_index);
@@ -210,24 +212,24 @@ void kfence_report_error(unsigned long a
case KFENCE_ERROR_UAF:
pr_err("BUG: KFENCE: use-after-free %s in %pS\n\n", get_access_type(is_write),
(void *)stack_entries[skipnr]);
- pr_err("Use-after-free %s at 0x" PTR_FMT " (in kfence-#%zd):\n",
+ pr_err("Use-after-free %s at 0x%p (in kfence-#%zd):\n",
get_access_type(is_write), (void *)address, object_index);
break;
case KFENCE_ERROR_CORRUPTION:
pr_err("BUG: KFENCE: memory corruption in %pS\n\n", (void *)stack_entries[skipnr]);
- pr_err("Corrupted memory at 0x" PTR_FMT " ", (void *)address);
+ pr_err("Corrupted memory at 0x%p ", (void *)address);
print_diff_canary(address, 16, meta);
pr_cont(" (in kfence-#%zd):\n", object_index);
break;
case KFENCE_ERROR_INVALID:
pr_err("BUG: KFENCE: invalid %s in %pS\n\n", get_access_type(is_write),
(void *)stack_entries[skipnr]);
- pr_err("Invalid %s at 0x" PTR_FMT ":\n", get_access_type(is_write),
+ pr_err("Invalid %s at 0x%p:\n", get_access_type(is_write),
(void *)address);
break;
case KFENCE_ERROR_INVALID_FREE:
pr_err("BUG: KFENCE: invalid free in %pS\n\n", (void *)stack_entries[skipnr]);
- pr_err("Invalid free of 0x" PTR_FMT " (in kfence-#%zd):\n", (void *)address,
+ pr_err("Invalid free of 0x%p (in kfence-#%zd):\n", (void *)address,
object_index);
break;
}
@@ -242,7 +244,7 @@ void kfence_report_error(unsigned long a
/* Print report footer. */
pr_err("\n");
- if (IS_ENABLED(CONFIG_DEBUG_KERNEL) && regs)
+ if (no_hash_pointers && regs)
show_regs(regs);
else
dump_stack_print_info(KERN_ERR);
_
Patches currently in -mm which might be from elver@xxxxxxxxxx are
mm-add-kernel-electric-fence-infrastructure-fix.patch
mm-add-kernel-electric-fence-infrastructure-fix-2.patch
mm-add-kernel-electric-fence-infrastructure-fix-3.patch
mm-add-kernel-electric-fence-infrastructure-fix-4.patch
mm-add-kernel-electric-fence-infrastructure-fix-5.patch
x86-kfence-enable-kfence-for-x86-fix.patch
arm64-kfence-enable-kfence-for-arm64.patch
arm64-kfence-enable-kfence-for-arm64-fix.patch
kfence-use-pt_regs-to-generate-stack-trace-on-faults.patch
kfence-documentation-add-kfence-documentation.patch
kfence-documentation-add-kfence-documentation-fix.patch
kfence-add-test-suite.patch
kfence-add-test-suite-fix.patch
kfence-add-test-suite-fix-2.patch
maintainers-add-entry-for-kfence.patch
kfence-report-sensitive-information-based-on-no_hash_pointers.patch
