[PATCH 1/2] arm64: Get 'info->page_offset' from PT_LOAD segments to support KASLR boot cases

[Bhupesh Sharma <bhsharma@redhat.com>]

The existing methodology to obtain 'info->page_offset' from reading
_stext symbol (from kallsyms) doesn't work well in KASLR boot cases on
arm64 machines as the PAGE_OFFSET (or the virtual address which
indicates the start of the linear region) can be randomized as well
on basis of the kaslr-seed.

Since the value of PAGE_OFFSET inside the kernel is randomized in such
cases and there is no existing mechanism of conveying this value from
kernel-space to user-space, so we can use the method used by archs like
x86_64 to generate the 'info->page_offset' value from the PT_LOAD
segments by subtracting the phy_addr from virt_addr of a PT_LOAD
segment.

This approach works fine both with KASLR and non-KASLR boot cases.

I tested this on my qualcomm-amberwing board. Here are some logs from
the KASLR boot cases:

- Verify that the EFI firmware supports 'kaslr-seed':

	chosen {
		kaslr-seed = <0x0 0x0>;
		<..snip..>
	};

- Verify that '--mem-usage' works well after this fix as well (I used
  kernel 4.18.0-rc4+ for my checks):

The kernel version is not supported.
The makedumpfile operation may be incomplete.

TYPE		PAGES			EXCLUDABLE	DESCRIPTION
----------------------------------------------------------------------
ZERO		4396            	yes		Pages filled
with zero
NON_PRI_CACHE	27859           	yes		Cache pages
without private flag
PRI_CACHE	18490           	yes		Cache pages with
private flag
USER		2728            	yes		User process
pages
FREE		1465848         	yes		Free pages
KERN_DATA	18537           	no		Dumpable kernel
data

page size:		65536
Total pages on system:	1537858
Total size on system:	100785061888     Byte

Signed-off-by: Bhupesh Sharma <bhsharma@redhat.com>
---
 arch/arm64.c   | 23 ++++++++++++++++++-----
 common.h       |  1 +
 makedumpfile.h |  1 +
 3 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/arch/arm64.c b/arch/arm64.c
index 2fd3e1874376..9e8c77c76935 100644
--- a/arch/arm64.c
+++ b/arch/arm64.c
@@ -265,6 +265,9 @@ get_xen_info_arm64(void)
 int
 get_versiondep_info_arm64(void)
 {
+	int i;
+	unsigned long long phys_start;
+	unsigned long long virt_start;
 	ulong _stext;
 
 	_stext = get_stext_symbol();
@@ -289,12 +292,22 @@ get_versiondep_info_arm64(void)
 		return FALSE;
 	}
 
-	info->page_offset = (0xffffffffffffffffUL) << (va_bits - 1);
-
-	DEBUG_MSG("page_offset=%lx, va_bits=%d\n", info->page_offset,
-			va_bits);
+	if (get_num_pt_loads()) {
+		for (i = 0;
+			get_pt_load(i, &phys_start, NULL, &virt_start, NULL);
+			i++) {
+			if (virt_start != NOT_KV_ADDR
+					&& virt_start < __START_KERNEL_map
+					&& phys_start != NOT_PADDR && phys_start != NOT_PADDR_ARM64) {
+				info->page_offset = virt_start - phys_start;
+				DEBUG_MSG("info->page_offset: %lx, VA_BITS: %d\n",
+						info->page_offset, va_bits);
+				return TRUE;
+			}
+		}
+	}
 
-	return TRUE;
+	return FALSE;
 }
 
 /*
diff --git a/common.h b/common.h
index 6e2f657a79c7..a8181777dbb7 100644
--- a/common.h
+++ b/common.h
@@ -48,6 +48,7 @@
 #define NOT_MEMMAP_ADDR	(0x0)
 #define NOT_KV_ADDR	(0x0)
 #define NOT_PADDR	(ULONGLONG_MAX)
+#define NOT_PADDR_ARM64	(0x0000000010a80000UL)
 #define BADADDR  	((ulong)(-1))
 
 #endif  /* COMMON_H */
diff --git a/makedumpfile.h b/makedumpfile.h
index 5ff94b8e4ac6..5297279f0f3b 100644
--- a/makedumpfile.h
+++ b/makedumpfile.h
@@ -2020,6 +2020,7 @@ struct domain_list {
 #define MFNS_PER_FRAME		(info->page_size / sizeof(unsigned long))
 
 #ifdef __aarch64__
+#define __START_KERNEL_map		(0xffffffff80000000UL)
 unsigned long long kvtop_xen_arm64(unsigned long kvaddr);
 #define kvtop_xen(X)	kvtop_xen_arm64(X)
 #endif /* aarch64 */
-- 
2.7.4


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