coredump: select memory types to include

Currently /proc/<pid>/coredump_filter determines what types of memory
are included in a coredump produced by <pid>. This is fairly static. The
coredump server has no easy way to configure what memory to dump even
though it can figure out all the necessary details to make an informed
decision.

Add a new COREDUMP_MEMORY_TYPES feature bit. If the coredump server
raises it the kernel will dump memory types raised in the
coredump_ack->memory_types member. Zero is valid and causes the creation
of a coredump that just includes the program headers and notes but no
memory apart from the mappings that are always dumped.

struct coredump_req gains @memory_types which is set to the default
memory types that are included in the coredump. This can be overridden by
raising bits in coredump_ack->memory_types. It also gains
@memory_types_mask which contains a bitmask of all memory types the
kernel knows about. A coredump server may only raise bits in
coredump_ack->memory_types that are raised in
coredump_req->memory_types_mask.

struct coredump_ack grows too. If COREDUMP_MEMORY_TYPES is raised in
@mask the kernel dumps the memory types set in the @memory_types mask.
Zero is valid and dumps no memory apart from the mappings that are
always dumped. A coredump server wanting to add or drop memory types
instead of outright replacing it should simply copy
coredump_req->memory_types and then mask off or raise types as needed.

@memory_types must be zero if COREDUMP_MEMORY_TYPES isn't raised.
COREDUMP_MEMORY_TYPES requires COREDUMP_KERNEL and an ack of at least
COREDUMP_ACK_SIZE_VER1 bytes.

Link: https://patch.msgid.link/20260821-work-coredump-filter-v1-1-91f9a73ef03e@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

1 files changed, 68 insertions, 2 deletions

diff --git a/include/uapi/linux/coredump.h b/include/uapi/linux/coredump.h
index f3771861ca48..6d0c53b534ea 100644
--- a/include/uapi/linux/coredump.h
+++ b/include/uapi/linux/coredump.h
@@ -16,6 +16,9 @@
  *                    requires COREDUMP_KERNEL
  * @COREDUMP_SPARSE: describe the holes in the coredump as zero records
  *                   instead of transferring them; requires COREDUMP_RECORDS
+ * @COREDUMP_MEMORY_TYPES: dump the memory types in
+ *                          coredump_ack->memory_types instead of the ones
+ *                          the task selected; requires COREDUMP_KERNEL
  */
 enum {
 	COREDUMP_KERNEL		= (1ULL << 0),
@@ -24,6 +27,37 @@ enum {
 	COREDUMP_WAIT		= (1ULL << 3),
 	COREDUMP_RECORDS	= (1ULL << 4),
 	COREDUMP_SPARSE		= (1ULL << 5),
+	COREDUMP_MEMORY_TYPES	= (1ULL << 6),
+};
+
+/**
+ * coredump memory types
+ * @COREDUMP_MEMORY_ANON_PRIVATE: anonymous private memory
+ * @COREDUMP_MEMORY_ANON_SHARED: anonymous shared memory
+ * @COREDUMP_MEMORY_FILE_PRIVATE: file-backed private memory
+ * @COREDUMP_MEMORY_FILE_SHARED: file-backed shared memory
+ * @COREDUMP_MEMORY_ELF_HEADERS: the first page of a file-backed private
+ *                               mapping that starts an ELF file
+ * @COREDUMP_MEMORY_HUGETLB_PRIVATE: hugetlb private memory
+ * @COREDUMP_MEMORY_HUGETLB_SHARED: hugetlb shared memory
+ * @COREDUMP_MEMORY_DAX_PRIVATE: DAX private memory
+ * @COREDUMP_MEMORY_DAX_SHARED: DAX shared memory
+ *
+ * A bitmask of memory types a coredump may request to be included. New
+ * memory type bits must ensure that they do not steal memory from an
+ * existing one so a coredump server will continue to get the same
+ * coredumps even if a new bit is introduced.
+ */
+enum {
+	COREDUMP_MEMORY_ANON_PRIVATE	= (1ULL << 0),
+	COREDUMP_MEMORY_ANON_SHARED	= (1ULL << 1),
+	COREDUMP_MEMORY_FILE_PRIVATE	= (1ULL << 2),
+	COREDUMP_MEMORY_FILE_SHARED	= (1ULL << 3),
+	COREDUMP_MEMORY_ELF_HEADERS	= (1ULL << 4),
+	COREDUMP_MEMORY_HUGETLB_PRIVATE	= (1ULL << 5),
+	COREDUMP_MEMORY_HUGETLB_SHARED	= (1ULL << 6),
+	COREDUMP_MEMORY_DAX_PRIVATE	= (1ULL << 7),
+	COREDUMP_MEMORY_DAX_SHARED	= (1ULL << 8),
 };
 
 /**
@@ -31,6 +65,8 @@ enum {
  * @size: size of struct coredump_req
  * @size_ack: known size of struct coredump_ack on this kernel
  * @mask: supported features
+ * @memory_types: the memory types the task selected
+ * @memory_types_mask: the memory types this kernel knows
  *
  * When a coredump happens the kernel will connect to the coredump
  * socket and send a coredump request to the coredump server. The @size
@@ -49,15 +85,27 @@ enum {
  * struct coredump_ack the kernel knows. Userspace may only send up to
  * coredump_req->size_ack bytes to the kernel and must set
  * coredump_ack->size accordingly.
+ *
+ * @memory_types is set to the default memory types that are included in
+ * the coredump. This can be overridden by raising bits in
+ * coredump_ack->memory_types.
+ *
+ * @memory_types_mask contains a bitmask of all memory types the kernel
+ * knows about. A coredump server may only raise bits in
+ * coredump_ack->memory_types that are raised in
+ * coredump_req->memory_types_mask.
  */
 struct coredump_req {
 	__u32 size;
 	__u32 size_ack;
 	__u64 mask;
+	__u64 memory_types;
+	__u64 memory_types_mask;
 };
 
 enum {
 	COREDUMP_REQ_SIZE_VER0 = 16U, /* size of first published struct */
+	COREDUMP_REQ_SIZE_VER1 = 32U, /* memory_types and memory_types_mask added */
 };
 
 /**
@@ -65,6 +113,8 @@ enum {
  * @size: size of the struct
  * @spare: unused
  * @mask: features kernel is supposed to use
+ * @memory_types: memory types to dump, only with COREDUMP_MEMORY_TYPES
+ *                 in @mask
  *
  * The @size member must be set to the size of struct coredump_ack. It
  * may never exceed what the kernel returned in coredump_req->size_ack
@@ -74,15 +124,30 @@ enum {
  * The @mask member must be set to the features the coredump server
  * wants the kernel to use. Only bits the kernel returned in
  * coredump_req->mask may be set.
+ *
+ * If COREDUMP_MEMORY_TYPES is raised in @mask the kernel dumps the
+ * memory types set in the @memory_types mask. Zero is valid and dumps
+ * no memory apart from the mappings that are always dumped.
+ *
+ * Note that memory a task excluded via MADV_DONTDUMP is always left
+ * out. A coredump server wanting to add or drop memory types instead of
+ * outright replacing it should simply copy coredump_req->memory_types
+ * and then mask off or raise types as needed.
+ *
+ * Note that @memory_types must be zero if COREDUMP_MEMORY_TYPES isn't
+ * raised. COREDUMP_MEMORY_TYPES requires COREDUMP_KERNEL and an ack of
+ * at least COREDUMP_ACK_SIZE_VER1 bytes.
  */
 struct coredump_ack {
 	__u32 size;
 	__u32 spare;
 	__u64 mask;
+	__u64 memory_types;
 };
 
 enum {
 	COREDUMP_ACK_SIZE_VER0 = 16U, /* size of first published struct */
+	COREDUMP_ACK_SIZE_VER1 = 24U, /* memory_types added */
 };
 
 /**
@@ -90,11 +155,12 @@ enum {
  *
  * The kernel will place a single byte on the coredump socket. The
  * markers notify userspace whether the coredump ack succeeded or
- * failed.
+ * failed. After any marker other than COREDUMP_MARK_REQACK the kernel
+ * closes the connection and no coredump is generated.
  *
  * @COREDUMP_MARK_MINSIZE: the provided coredump_ack size was too small
  * @COREDUMP_MARK_MAXSIZE: the provided coredump_ack size was too big
- * @COREDUMP_MARK_UNSUPPORTED: the provided coredump_ack mask was invalid
+ * @COREDUMP_MARK_UNSUPPORTED: the provided coredump_ack mask or memory types were invalid
  * @COREDUMP_MARK_CONFLICTING: the provided coredump_ack mask has conflicting options
  * @COREDUMP_MARK_REQACK: the coredump request and ack was successful
  * @__COREDUMP_MARK_MAX: the maximum coredump mark value