Thank you for the patch, XingYang.
On Sun, Sep 22, 2024 at 1:08 AM <root@xxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
From: 1127955419@xxxxxx
To: devel@xxxxxxxxxxxxxxxxxxxxxxxxxxx, ltao@xxxxxxxxxx
Cc: Li XingYang <1127955419@xxxxxx>, Zach Wade <zachwade.k@xxxxxxxxx>
Bcc:
Date: Sun, 22 Sep 2024 01:00:29 +0800
Subject: [PATCH] X86 64: fix the method for determining whether to enable kalsr
From: Li XingYang <1127955419@xxxxxx>
The recently commit 6752571d8d78 fixed the issue where linux kernel with
223b5e57d0d5 ("mm/execmem, arch: convert remaining overrides of module_alloc to execmem")
could not load crash, but it did not work in the following two situations:
1： Kernel enables KASAN
2： The kernel set CONFIG_RANDOMIZE_BASE but not set CONFIG_RANDOMIZE_MEMORY
crash: seek error: kernel virtual address: ffffffff826bb418 type: "page_offset_base"
In both cases, kaslr_regions will not be exported in /proc/kallsyms,
but kaslr_get_random_long will still be exported in /proc/kallsyms.
So use kaslr_get_random_long instead of kaslr_degions
Determine whether to enable kalsr
The kaslr_get_random_long() is not exported by EXPORT_SYMBOL(), not sure if this could be optimized out(elimited) by the compiler, we have observed the kaslr_regions symbol could be optimized out in some kernels.
But anyway, I do not have a better solution for the time being. So I agree to this change: Ack.
BTW: The following functions in the kernel really misled me.
static inline bool kaslr_enabled(void)
{
return IS_ENABLED(CONFIG_RANDOMIZE_MEMORY) &&
!!(boot_params.hdr.loadflags & KASLR_FLAG);
}
/*
* Apply no randomization if KASLR was disabled at boot or if KASAN
* is enabled. KASAN shadow mappings rely on regions being PGD aligned.
*/
static inline bool kaslr_memory_enabled(void)
{
return kaslr_enabled() && !IS_ENABLED(CONFIG_KASAN);
}
{
return IS_ENABLED(CONFIG_RANDOMIZE_MEMORY) &&
!!(boot_params.hdr.loadflags & KASLR_FLAG);
}
/*
* Apply no randomization if KASLR was disabled at boot or if KASAN
* is enabled. KASAN shadow mappings rely on regions being PGD aligned.
*/
static inline bool kaslr_memory_enabled(void)
{
return kaslr_enabled() && !IS_ENABLED(CONFIG_KASAN);
}
Thanks
Lianbo
Signed-off-by: Li XingYang <1127955419@xxxxxx>
Signed-off-by: Zach Wade <zachwade.k@xxxxxxxxx>
---
symbols.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/symbols.c b/symbols.c
index 69a1fbb..02359a4 100644
--- a/symbols.c
+++ b/symbols.c
@@ -619,7 +619,7 @@ strip_symbol_end(const char *name, char *buf)
* or in /proc/kallsyms on a live system.
*
* Setting KASLR_CHECK will trigger a search for "module_load_offset"
- * or "kaslr_regions" during the initial symbol sort operation, and
+ * or "kaslr_get_random_long" during the initial symbol sort operation, and
* if found, will set (RELOC_AUTO|KASLR). On live systems, the search
* is done here by checking /proc/kallsyms.
*/
@@ -646,7 +646,7 @@ kaslr_init(void)
st->_stext_vmlinux = UNINITIALIZED;
if (ACTIVE() && /* Linux 3.15 */
- ((symbol_value_from_proc_kallsyms("kaslr_regions") != BADVAL) ||
+ ((symbol_value_from_proc_kallsyms("kaslr_get_random_long") != BADVAL) ||
(symbol_value_from_proc_kallsyms("module_load_offset") != BADVAL))) {
kt->flags2 |= (RELOC_AUTO|KASLR);
st->_stext_vmlinux = UNINITIALIZED;
@@ -14253,8 +14253,8 @@ numeric_forward(const void *P_x, const void *P_y)
st->_stext_vmlinux = valueof(y);
}
if (kt->flags2 & KASLR_CHECK) {
- if (STREQ(x->name, "kaslr_regions") ||
- STREQ(y->name, "kaslr_regions") ||
+ if (STREQ(x->name, "kaslr_get_random_long") ||
+ STREQ(y->name, "kaslr_get_random_long") ||
STREQ(x->name, "module_load_offset") ||
STREQ(y->name, "module_load_offset")) {
kt->flags2 &= ~KASLR_CHECK;
--
2.46.1
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