[PATCH v2 0/2] arm64: fix crash when reading /proc/kcore

This is a follow-up to patches from zhonjiang [0] and myself [1] that aim
to solve a problem in the kcore code, which gets confused by the presence
of block mappings in the vmalloc region.

While fixing the crash is quite straight forward [2], we need to tweak
the kcore code itself to ensure that it operates correctly on arm64.
Fortunately, we can achieve this with two very simple changes:

- replace a call to is_vmalloc_or_module_addr() in read_kcore() with a
  comparison of the kclist type field (#1)
- enable CONFIG_ARCH_PROC_KCORE_TEXT for arm64 (#2)

[0] http://marc.info/?l=linux-mm&m=149632393629295&w=2
[1] http://marc.info/?l=linux-mm&m=149685966530180&w=2
[2] http://marc.info/?l=linux-mm&m=149694975123959&w=2

v2: add acks only, no code changes

Will, Catalin, could you queue these for v4.13 please?

Ard Biesheuvel (2):
  fs/proc: kcore: use kcore_list type to check for vmalloc/module
    address
  arm64: mm: select CONFIG_ARCH_PROC_KCORE_TEXT

 arch/arm64/Kconfig | 3 +++
 fs/proc/kcore.c    | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

-- 
2.7.4

Instead of passing each start address into is_vmalloc_or_module_addr()
to decide whether it falls into either the VMALLOC or the MODULES region,
we can simply check the type field of the current kcore_list entry, since
it will be set to KCORE_VMALLOC based on exactly the same conditions.

As a bonus, when reading the KCORE_TEXT region on architectures that have
one, this will avoid using vread() on the region if it happens to intersect
with a KCORE_VMALLOC region. This is due the fact that the KCORE_TEXT
region is the first one to be added to the kcore region list.

Reported-by: Tan Xiaojun <redacted>
Tested-by: Tan Xiaojun <redacted>
Tested-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Laura Abbott <redacted>
Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Ard Biesheuvel <redacted>
---
 fs/proc/kcore.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
index 4ee55274f155..45629f4b5402 100644
--- a/fs/proc/kcore.c
+++ b/fs/proc/kcore.c

@@ -504,7 +504,7 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 		if (&m->list == &kclist_head) {
 			if (clear_user(buffer, tsz))
 				return -EFAULT;
-		} else if (is_vmalloc_or_module_addr((void *)start)) {
+		} else if (m->type == KCORE_VMALLOC) {
 			vread(buf, (char *)start, tsz);
 			/* we have to zero-fill user buffer even if no read */
 			if (copy_to_user(buffer, buf, tsz))

-- 
2.7.4

To avoid issues with the /proc/kcore code getting confused about the
kernels block mappings in the VMALLOC region, enable the existing
facility that describes the [_text, _end) interval as a separate
KCORE_TEXT region, which supersedes the KCORE_VMALLOC region that
it intersects with on arm64.

Reported-by: Tan Xiaojun <redacted>
Tested-by: Tan Xiaojun <redacted>
Tested-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Laura Abbott <redacted>
Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Ard Biesheuvel <redacted>
---
 arch/arm64/Kconfig | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index b2024db225a9..233611abffb2 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig

@@ -244,6 +244,9 @@ config PGTABLE_LEVELS
 config ARCH_SUPPORTS_UPROBES
 	def_bool y
 
+config ARCH_PROC_KCORE_TEXT
+	def_bool y
+
 source "init/Kconfig"
 
 source "kernel/Kconfig.freezer"

-- 
2.7.4