[RFC PATCH v2 4/6] arm64: signal: Allocate extra sigcontext space as needed
Dave Martin
Dave.Martin at arm.com
Wed Apr 12 13:01:13 EDT 2017
This patch modifies the context block allocator to create an
extra_context expansion block as necessary, and adds the necessary
code to populate, parse and decode this block.
Signed-off-by: Dave Martin <Dave.Martin at arm.com>
---
arch/arm64/include/uapi/asm/sigcontext.h | 27 ++++++++
arch/arm64/kernel/signal.c | 111 ++++++++++++++++++++++++++-----
2 files changed, 120 insertions(+), 18 deletions(-)
diff --git a/arch/arm64/include/uapi/asm/sigcontext.h b/arch/arm64/include/uapi/asm/sigcontext.h
index 1328a2c..b5e2523 100644
--- a/arch/arm64/include/uapi/asm/sigcontext.h
+++ b/arch/arm64/include/uapi/asm/sigcontext.h
@@ -80,4 +80,31 @@ struct esr_context {
__u64 esr;
};
+/*
+ * Pointer to extra space for additional structures that don't fit in
+ * sigcontext.__reserved[]. Note:
+ *
+ * 1) fpsimd_context, esr_context and extra_context must be placed in
+ * sigcontext.__reserved[] if present. They cannot be placed in the
+ * extra space. Any other record can be placed either in the extra
+ * space or in sigcontext.__reserved[].
+ *
+ * 2) There must not be more than one extra_context.
+ *
+ * 3) If extra_context is present, it must be followed immediately in
+ * sigcontext.__reserved[] by the terminating null _aarch64_ctx (i.e.,
+ * extra_context must be the last record in sigcontext.__reserved[]
+ * except for the terminator).
+ *
+ * 4) The extra space must itself be terminated with a null
+ * _aarch64_ctx.
+ */
+#define EXTRA_MAGIC 0x45585401
+
+struct extra_context {
+ struct _aarch64_ctx head;
+ void __user *data; /* 16-byte aligned pointer to extra space */
+ __u32 size; /* size in bytes of the extra space */
+};
+
#endif /* _UAPI__ASM_SIGCONTEXT_H */
diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index 47592af..95547e1 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -25,6 +25,7 @@
#include <linux/freezer.h>
#include <linux/stddef.h>
#include <linux/uaccess.h>
+#include <linux/sizes.h>
#include <linux/string.h>
#include <linux/tracehook.h>
#include <linux/ratelimit.h>
@@ -56,18 +57,27 @@ struct rt_sigframe_user_layout {
unsigned long fpsimd_offset;
unsigned long esr_offset;
+ unsigned long extra_offset;
unsigned long end_offset;
};
+#define BASE_SIGFRAME_SIZE round_up(sizeof(struct rt_sigframe), 16)
+#define TERMINATOR_SIZE round_up(sizeof(struct _aarch64_ctx), 16)
+#define EXTRA_CONTEXT_SIZE round_up(sizeof(struct extra_context), 16)
+
static void init_user_layout(struct rt_sigframe_user_layout *user)
{
+ const size_t reserved_size =
+ sizeof(user->sigframe->uc.uc_mcontext.__reserved);
+
memset(user, 0, sizeof(*user));
user->size = offsetof(struct rt_sigframe, uc.uc_mcontext.__reserved);
- user->limit = user->size +
- sizeof(user->sigframe->uc.uc_mcontext.__reserved) -
- round_up(sizeof(struct _aarch64_ctx), 16);
- /* ^ reserve space for terminator */
+ user->limit = user->size + reserved_size;
+
+ user->limit -= TERMINATOR_SIZE;
+ user->limit -= EXTRA_CONTEXT_SIZE;
+ /* Reserve space for extension and terminator ^ */
}
static size_t sigframe_size(struct rt_sigframe_user_layout const *user)
@@ -75,6 +85,48 @@ static size_t sigframe_size(struct rt_sigframe_user_layout const *user)
return round_up(max(user->size, sizeof(struct rt_sigframe)), 16);
}
+/* Sanity limit on the maximum size of signal frame we'll try to generate. */
+/* This is NOT ABI. */
+#define SIGFRAME_MAXSZ SZ_64K
+
+static int __sigframe_alloc(struct rt_sigframe_user_layout *user,
+ unsigned long *offset, size_t size, bool extend)
+{
+ size_t padded_size = round_up(size, 16);
+
+ if (padded_size > user->limit - user->size &&
+ !user->extra_offset &&
+ extend) {
+ int ret;
+
+ ret = __sigframe_alloc(user, &user->extra_offset,
+ sizeof(struct extra_context), false);
+ if (ret)
+ return ret;
+
+ /*
+ * Further allocations must go after the fixed-size
+ * part of the signal frame:
+ */
+ user->size = BASE_SIGFRAME_SIZE;
+
+ /*
+ * Allow expansion up to SIGFRAME_MAXSZ, ensuring space for
+ * the terminator:
+ */
+ user->limit = SIGFRAME_MAXSZ - TERMINATOR_SIZE;
+ }
+
+ /* Still not enough space? Bad luck! */
+ if (padded_size > user->limit - user->size)
+ return -ENOMEM;
+
+ *offset = user->size;
+ user->size += padded_size;
+
+ return 0;
+}
+
/*
* Allocate space for an optional record of <size> bytes in the user
* signal frame. The offset from the signal frame base address to the
@@ -83,11 +135,24 @@ static size_t sigframe_size(struct rt_sigframe_user_layout const *user)
static int sigframe_alloc(struct rt_sigframe_user_layout *user,
unsigned long *offset, size_t size)
{
- size_t padded_size = round_up(size, 16);
+ return __sigframe_alloc(user, offset, size, true);
+}
- *offset = user->size;
- user->size += padded_size;
+/* Allocate the null terminator record and prevent further allocations */
+static int sigframe_alloc_end(struct rt_sigframe_user_layout *user)
+{
+ int ret;
+
+ /* Un-reserve the space reserved for the terminator: */
+ user->limit += TERMINATOR_SIZE;
+
+ ret = sigframe_alloc(user, &user->end_offset,
+ sizeof(struct _aarch64_ctx));
+ if (ret)
+ return ret;
+ /* Prevent further allocation: */
+ user->limit = user->size;
return 0;
}
@@ -314,17 +379,7 @@ static int setup_sigframe_layout(struct rt_sigframe_user_layout *user)
return err;
}
- /*
- * Allocate space for the terminator record.
- * HACK: here we undo the reservation of space for the end record.
- * This bodge should be replaced with a cleaner approach later on.
- */
- user->limit = offsetof(struct rt_sigframe, uc.uc_mcontext.__reserved) +
- sizeof(user->sigframe->uc.uc_mcontext.__reserved);
-
- err = sigframe_alloc(user, &user->end_offset,
- sizeof(struct _aarch64_ctx));
- return err;
+ return sigframe_alloc_end(user);
}
@@ -365,6 +420,26 @@ static int setup_sigframe(struct rt_sigframe_user_layout *user,
__put_user_error(current->thread.fault_code, &esr_ctx->esr, err);
}
+ if (err == 0 && user->extra_offset) {
+ struct extra_context __user *extra =
+ apply_user_offset(user, user->extra_offset);
+ struct _aarch64_ctx __user *end =
+ (struct _aarch64_ctx __user *)((char __user *)extra +
+ round_up(sizeof(*extra), 16));
+ void __user *extra_data =
+ apply_user_offset(user, BASE_SIGFRAME_SIZE);
+ u32 extra_size = round_up(user->size, 16) - BASE_SIGFRAME_SIZE;
+
+ __put_user_error(EXTRA_MAGIC, &extra->head.magic, err);
+ __put_user_error(sizeof(*extra), &extra->head.size, err);
+ __put_user_error(extra_data, &extra->data, err);
+ __put_user_error(extra_size, &extra->size, err);
+
+ /* Add the terminator */
+ __put_user_error(0, &end->magic, err);
+ __put_user_error(0, &end->size, err);
+ }
+
/* set the "end" magic */
if (err == 0) {
struct _aarch64_ctx __user *end =
--
2.1.4
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