From: Matthias Kruk <m@m10k.eu>
Date: Wed, 29 Jul 2020 00:54:42 +0000 (+0900)
Subject: kernel: Grow the userspace stack if an application runs out of stack space
X-Git-Url: https://git.corax.cc/?a=commitdiff_plain;h=refs%2Fheads%2Fuserstack;p=corax

kernel: Grow the userspace stack if an application runs out of stack space
---

diff --git a/config.h b/config.h
index 7cad81f..eeef1b2 100644
--- a/config.h
+++ b/config.h
@@ -29,6 +29,7 @@
 #define CONFIG_KERNEL_STACK_BASE    ((void*)0xffffe000)
 #endif /* !__ASSEMBLY_SOURCE */
 #define CONFIG_USER_STACK_SIZE      4096
+#define CONFIG_USER_STACK_LIMIT     (16 * 1048576)
 #define CONFIG_PROC_MAXTASKS        8
 #define CONFIG_MUTEX_WAITQLEN       8
 #define CONFIG_SEM_WAITQLEN         8
diff --git a/kernel/arch/interrupt.c b/kernel/arch/interrupt.c
index 60e3399..fdd7346 100644
--- a/kernel/arch/interrupt.c
+++ b/kernel/arch/interrupt.c
@@ -172,6 +172,24 @@ void _int_handle(stack_frame_t ctx)
     return;
 }
 
+static int _handle_pagefault(process_t *proc, task_t *task, u32_t addr)
+{
+	pg_dir_t *pd;
+	int ret_val;
+
+	ret_val = process_get_pagedir(proc, &pd);
+
+	if(!ret_val) {
+		/*
+		 * pg_dir_grow_ustack() checks the address and only grows the
+		 * stack if would not exceed the statically defined limit.
+		 */
+		ret_val = pg_dir_grow_ustack(pd, (void*)addr);
+	}
+
+	return(ret_val);
+}
+
 void _exc_handle(stack_frame_t ctx)
 {
 	process_t *cproc;
@@ -184,7 +202,7 @@ void _exc_handle(stack_frame_t ctx)
 		/* kernel bug */
 
 		dbg_printf("Exception %u [%s] occurred. Error code 0x%08x.\n",
-				   ctx.intn, ctx.intn < EXC_MAX ? _exc_name[ctx.intn] : 0, ctx.error);
+			   ctx.intn, ctx.intn < EXC_MAX ? _exc_name[ctx.intn] : 0, ctx.error);
 		dbg_printf("In context %p [pid %u]\n", cproc, process_get_id(cproc));
 		dbg_printf("Fault in 0x%02x:%08x; EFLAGS = 0x%08x\n", ctx.cs, ctx.eip, ctx.eflags);
 
@@ -207,20 +225,22 @@ void _exc_handle(stack_frame_t ctx)
 
 		int sig;
 
-		dbg_printf("User-mode exception %u at 0x%08x\n", ctx.intn, ctx.eip);
+		dbg_printf("User-mode exception %u in pid %u at 0x%08x\n",
+			   ctx.intn, process_get_id(cproc), ctx.eip);
 
 		if(ctx.intn == EXC_PAGEFAULT) {
 			u32_t cr2;
-			pg_dir_t *pd;
 
 			asm volatile("movl %%cr2, %%eax; movl %%eax, %0" : "=r"(cr2));
 			dbg_printf("CR2: 0x%08x\n", cr2);
 
-			if(process_get_pagedir(cproc, &pd) == 0) {
-				pg_fault_debug(pd, (void*)cr2);
+			if(_handle_pagefault(cproc, ctask, cr2) >= 0) {
+				goto skip_signal;
 			}
 		}
 
+		for(;;);
+
 		switch(ctx.intn) {
 		default:
 		case EXC_DEBUG:
@@ -267,7 +287,8 @@ void _exc_handle(stack_frame_t ctx)
 		task_signal_deliver(ctask, &ctx, sig, NULL);
 	}
 
-    return;
+skip_signal:
+	return;
 }
 
 void _sys_handle(stack_frame_t ctx)
diff --git a/kernel/arch/paging.c b/kernel/arch/paging.c
index e02b668..0fec7d1 100644
--- a/kernel/arch/paging.c
+++ b/kernel/arch/paging.c
@@ -469,6 +469,77 @@ void* pg_dir_get_ustack(struct pagedir *pgdir)
 	return(ret_val);
 }
 
+void* pg_dir_get_ustack_top(struct pagedir *pgdir)
+{
+	struct region *reg;
+	void *ret_val;
+	int i;
+
+	for(ret_val = NULL, i = 0; i < CONFIG_PAGING_DIR_MAXREGIONS; i++) {
+		reg = pgdir->pd_regions[i];
+
+		if(reg->reg_type == REGION_STACK) {
+			ret_val = (char*)reg->reg_base + reg->reg_size;
+			break;
+		}
+	}
+
+	return(ret_val);
+}
+
+int pg_dir_grow_ustack(struct pagedir *pgdir, void *new_bottom)
+{
+	struct region *stack;
+	char *stack_max;
+	char *stack_min;
+	char *new_aligned;
+	int ret_val;
+	int i;
+
+	for(stack = NULL, i = 0; i < CONFIG_PAGING_DIR_MAXREGIONS; i++) {
+		if(pgdir->pd_regions[i]->reg_type == REGION_STACK) {
+			stack = pgdir->pd_regions[i];
+			break;
+		}
+	}
+
+	if(!stack) {
+		ret_val = -EBADFD;
+		goto gtfo;
+	}
+
+	stack_max = (char*)stack->reg_base + stack->reg_size;
+	stack_min = stack_max - CONFIG_USER_STACK_LIMIT;
+	new_aligned = (char*)((unsigned long)new_bottom &
+			      ~(stack->reg_pgsize - 1));
+
+	if(stack_min < new_aligned && new_aligned < stack_max) {
+		unsigned long map_size;
+
+		map_size = (unsigned long)stack->reg_base -
+			(unsigned long)new_aligned;
+
+		ret_val = pg_dir_map(pgdir, 0, new_aligned, map_size,
+				 stack->reg_attrs);
+
+		if(!ret_val) {
+			stack->reg_base = new_aligned;
+			stack->reg_size = (unsigned long)stack_max -
+				(unsigned long)new_aligned;
+
+			dbg_printf("%s: Mapped %u bytes at 0x%08x\n", __func__,
+				   map_size, new_aligned);
+			dbg_printf("%s: Stack is now at 0x%08x+0x%08x\n",
+				   __func__, stack->reg_base, stack->reg_size);
+		}
+	} else {
+		ret_val = -ENOMEM;
+	}
+
+gtfo:
+	return(ret_val);
+}
+
 int pg_dir_memcpy(struct pagedir *ddir, void *dvaddr,
 				  struct pagedir *sdir, void *svaddr, u32_t bytes)
 {
diff --git a/kernel/include/arch.h b/kernel/include/arch.h
index 161fed5..cfa3a20 100644
--- a/kernel/include/arch.h
+++ b/kernel/include/arch.h
@@ -234,6 +234,8 @@ void*   pg_dir_get_pdbr(pg_dir_t*);
 int     _pg_dir_vpxlate(pg_dir_t*, u32_t, u32_t*);
 void*   pg_dir_get_kstack(pg_dir_t*);
 void*   pg_dir_get_ustack(pg_dir_t*);
+void*   pg_dir_get_ustack_top(pg_dir_t*);
+int     pg_dir_grow_ustack(pg_dir_t*, void*);
 void*   pg_dir_sbrk(pg_dir_t*, i32_t);
 int     pg_dir_foreach_region(pg_dir_t*, int(*)(pg_dir_t*, struct region*, void*), void*);
 int     pg_dir_memcpy(pg_dir_t*, void*, pg_dir_t*, void*, u32_t);