Re: [Crash-utility] [PATCH v2 0/4] Generalize KASLR calculation and use it for KDUMPs
Hi Sergio,
A few initial comments/questions/concerns about this patch...
diff --git a/diskdump.c b/diskdump.c
index b08a46c..1ec4bcf 100644
--- a/diskdump.c
+++ b/diskdump.c
@@ -56,6 +56,7 @@ struct diskdump_data {
void **nt_prstatus_percpu;
uint num_prstatus_notes;
void **nt_qemu_percpu;
+ void **nt_qemucs_percpu;
uint num_qemu_notes;
/* page cache */
@@ -72,6 +73,7 @@ struct diskdump_data {
ulong *valid_pages;
ulong accesses;
ulong snapshot_task;
+ ulong kaslr_phys_base;
};
Generally speaking, there already is an sd->phys_base, and you've
added an nd->phys_base, but I don't understand why you also added
a new dd->kaslr_phys_base member and new diskdump_kaslr_phys_base()
function? Is there any reason that you can't continue to use the
currently-existing dd->sub_header_kdump->phys_base member and the
diskdump_phys_base() function? I just find the concept of a
"kaslr_phys_base" confusing, i.e., as if there are two different
types of phys_base in the kernel. Can you please try to utilize
the existing member and function?
Also related, your diskdump_kaslr_phys_base() and kdump_phys_base() functions
don't account for (return FALSE) with a legitimate phys_base value of 0.
In fact I have a sample RHEL7 ELF vmcore generated by virsh dump which
has a phys_base of 0. More on that below...
diff --git a/kaslr_helper.c b/kaslr_helper.c
index 1079863..5b71e3e 100644
--- a/kaslr_helper.c
+++ b/kaslr_helper.c
@@ -386,6 +386,9 @@ calc_kaslr_offset(ulong *kaslr_offset, ulong *phys_base)
if (KDUMP_DUMPFILE()) {
idtr = kdump_get_idtr();
cr3 = kdump_get_cr3();
+ } else if (DISKDUMP_DUMPFILE()) {
+ idtr = diskdump_get_idtr();
+ cr3 = diskdump_get_cr3();
All 4 of these new functions above can fail and return 0. Probably
unlikely, but shouldn't there be a FALSE return if either one is 0,
rather than continuing and using them?
} else {
return FALSE;
}
diff --git a/x86_64.c b/x86_64.c
index ed5985a..3c492e4 100644
--- a/x86_64.c
+++ b/x86_64.c
@@ -6632,8 +6632,15 @@ x86_64_calc_phys_base(void)
* Get relocation value from whatever dumpfile format is being used.
*/
- if (QEMU_MEM_DUMP_NO_VMCOREINFO() && KDUMP_DUMPFILE()) {
- if (kdump_phys_base(&phys_base)) {
+ if (QEMU_MEM_DUMP_NO_VMCOREINFO()) {
+ int ret;
+
+ if (KDUMP_DUMPFILE())
+ ret = kdump_phys_base(&phys_base);
+ else if (DISKDUMP_DUMPFILE())
+ ret = diskdump_kaslr_phys_base(&phys_base);
+
+ if (ret) {
machdep->machspec->phys_base = phys_base;
if (CRASHDEBUG(1))
fprintf(fp, "kdump-novmci: phys base: %lx\n",
--
2.14.3
This is where the "0 phys_base" issue comes into play. I think the section
above should do the same thing as the following "if (DISKDUMP_DUMPFILE())"
does, where diskump_phys_base() is only concerned if the dumpfile itself
is valid. It may return 0 as a phys_base, and that's OK, because it
unconditionally calls x86_64_virt_phys_base() -- which serves a dual
purpose, either to:
(1) verify it, or
(2) if it's bogus, it checks whether plus-or-minus 16MB works.
Thanks,
Dave