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[kernel,libc] Rewrite kernel brk/sbrk and stack_check, fix C library malloc #2128

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Dec 8, 2024
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[kernel,libc] Rewrite kernel brk/sbrk and stack_check, fix C library malloc #2128

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672981b
[kernel] Remove CONFIG_EXEC_LOW_STACK allowing stack below .data section
ghaerr Dec 7, 2024
c5ce605
[kernel,libc] Rewrite kernel brk/sbrk, fix C library malloc
ghaerr Dec 8, 2024
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41 changes: 17 additions & 24 deletions elks/arch/i86/kernel/process.c
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Original file line number Diff line number Diff line change
Expand Up @@ -43,34 +43,27 @@ int run_init_process_sptr(const char *cmd, char *sptr, int slen)
}

/*
* We only need to do this as long as we support old format binaries
* that grow stack and heap towards each other
* Check that SP is within proper range, called before every syscall.
*/
void stack_check(void)
{
segoff_t end = current->t_endbrk;

#ifdef CONFIG_EXEC_LOW_STACK
if (current->t_begstack <= current->t_enddata) { /* stack below heap?*/
if (current->t_regs.sp < end)
return;
end = 0;
} else
#endif
{
/* optional: check stack over min stack*/
if (current->t_regs.sp < current->t_begstack - current->t_minstack) {
if (current->t_minstack) /* display if protected stack*/
printk("(%P)STACK OUTSIDE PROTECTED LIMIT by %u\n",
current->t_begstack - current->t_minstack - current->t_regs.sp);
}

/* check stack overflow heap*/
if (current->t_regs.sp > end)
return;
segoff_t sp = current->t_regs.sp;
segoff_t brk = current->t_endbrk;
segoff_t stacklow = current->t_begstack - current->t_minstack;

if (sp < brk) {
printk("(%P)STACK OVERFLOW by %u\n", brk - sp);
printk("curbreak %u, SP %u\n", current->t_endbrk, current->t_regs.sp);
do_exit(SIGSEGV);
}
if (sp < stacklow) {
/* notification only, allow process to continue */
printk("(%P)STACK USING %u UNUSED HEAP\n", stacklow - sp);
}
if (sp > current->t_begstack) {
printk("(%P)STACK UNDERFLOW\n");
do_exit(SIGSEGV);
}
printk("(%P)STACK OVERFLOW by %u\n", end - current->t_regs.sp);
do_exit(SIGSEGV);
}

/*
Expand Down
51 changes: 30 additions & 21 deletions elks/arch/i86/mm/malloc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -230,49 +230,58 @@ void mm_get_usage (unsigned int * pfree, unsigned int * pused)

// User data segment functions

int sys_brk(segoff_t newbrk)
static int set_brk(segoff_t brk, int increment)
{
segoff_t newbrk = brk + increment;
segoff_t stacklow;

/***unsigned int memfree, memused;
mm_get_usage(&memfree, &memused);
printk("brk(%P): new %x, edat %x, ebrk %x, free %x sp %x, eseg %x, %d/%dK\n",
newbrk, current->t_enddata, current->t_endbrk,
current->t_regs.sp - current->t_endbrk,
current->t_regs.sp, current->t_endseg, memfree, memused);***/

if (newbrk < current->t_enddata)
if (newbrk < current->t_enddata) {
printk("(%P)SBRK %d FAIL, BELOW HEAP\n", increment);
return -ENOMEM;
}

if (current->t_begstack > current->t_endbrk) { /* stack above heap?*/
if (newbrk > current->t_begstack - current->t_minstack) {
printk("(%d)CAN'T EXPAND HEAP by %u\n",
current->pid, newbrk - (current->t_begstack - current->t_minstack));
return -ENOMEM;
}
stacklow = current->t_begstack - current->t_minstack;
if (newbrk > stacklow) {
printk("(%P)SBRK %d FAIL, OUT OF HEAP SPACE\n", increment);
return -ENOMEM;
}
#ifdef CONFIG_EXEC_LOW_STACK
if (newbrk > current->t_endseg)
if (newbrk > current->t_regs.sp) {
printk("(%P)SBRK %d FAIL, WOULD OVERWRITE STACK\n", increment);
return -ENOMEM;
#endif
current->t_endbrk = newbrk;
}

current->t_endbrk = newbrk;
return 0;
}

int sys_brk(segoff_t newbrk)
{
dprintk("(%P)BRK %u\n", newbrk);
return set_brk(newbrk, 0);
}

int sys_sbrk (int increment, segoff_t *pbrk)
int sys_sbrk(int increment, segoff_t *pbrk)
{
segoff_t brk = current->t_endbrk; /* always return start of old break*/
int err;

debug("sbrk incr %u pointer %04x curbreak %04x\n", increment, pbrk, brk);
if (increment)
dprintk("(%P)SBRK %d, curbreak %u, SP %u\n",
increment, current->t_endbrk, current->t_regs.sp);
err = verify_area(VERIFY_WRITE, pbrk, sizeof(*pbrk));
if (err)
return err;
if (increment) {
err = sys_brk(brk + increment);
if (err) return err;
}

/* FIXME test for brk+increment overflow/underflow here */
err = set_brk(brk, increment);
if (err)
return err;
put_user (brk, pbrk);
return 0;
}
Expand Down Expand Up @@ -307,12 +316,12 @@ int sys_fmemfree(unsigned short segment)
seg_free(seg);
return 0;
}
debug("sys_fmemfree: not owner %04x\n", segment);
printk("sys_fmemfree: not owner %04x\n", segment);
return -EACCES;
}
n = seg->all.next;
}
debug("sys_fmemfree: segment not found %04x\n", segment);
printk("sys_fmemfree: segment not found %04x\n", segment);
return -EINVAL;
}

Expand Down
28 changes: 0 additions & 28 deletions elks/fs/exec.c
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Original file line number Diff line number Diff line change
Expand Up @@ -266,18 +266,8 @@ static int execve_aout(struct inode *inode, struct file *filp, char *sptr, size_
if (esuph.msh_tbase != 0)
goto error_exec3;
base_data = esuph.msh_dbase;
#ifdef CONFIG_EXEC_LOW_STACK
if (base_data & 0xf)
goto error_exec3;
if (base_data != 0)
debug("EXEC: New type executable stack = %x\n", base_data);

if (add_overflow(min_len, base_data, &min_len)) /* adds stack size*/
goto error_exec3;
#else
if (base_data != 0)
goto error_exec3;
#endif
break;
#endif /* CONFIG_EXEC_MMODEL*/
default:
Expand All @@ -293,9 +283,6 @@ static int execve_aout(struct inode *inode, struct file *filp, char *sptr, size_
goto error_exec3;
case 1:
len = min_len;
#ifdef CONFIG_EXEC_LOW_STACK
if (!base_data)
#endif
{
stack = mh.minstack? mh.minstack: INIT_STACK;
if (add_overflow(len, stack, &len)) { /* add stack */
Expand Down Expand Up @@ -335,14 +322,6 @@ static int execve_aout(struct inode *inode, struct file *filp, char *sptr, size_
} else {
stack = INIT_STACK;
len = min_len;
#ifdef CONFIG_EXEC_LOW_STACK
if (base_data) {
if (add_overflow(len, INIT_HEAP, &len)) {
retval = -EFBIG;
goto error_exec3;
}
} else
#endif
{
if (add_overflow(len, INIT_HEAP + INIT_STACK, &len)) {
retval = -EFBIG;
Expand Down Expand Up @@ -495,14 +474,7 @@ static int execve_aout(struct inode *inode, struct file *filp, char *sptr, size_
currentp->t_enddata = (size_t)mh.dseg + (size_t)mh.bseg + base_data;
currentp->t_endseg = len;
currentp->t_regs.dx = currentp->t_minstack = stack;

#ifdef CONFIG_EXEC_LOW_STACK
currentp->t_begstack = ((base_data /* Just above the top of stack */
? base_data
: currentp->t_endseg) - slen) & ~1;
#else
currentp->t_begstack = (currentp->t_endseg - slen) & ~1; /* force even SP and argv */
#endif
fmemcpyb((char *)currentp->t_begstack, seg_data->base, sptr, ds, slen);

finalize_exec(inode, seg_code, seg_data, (word_t)mh.entry, 0);
Expand Down
9 changes: 5 additions & 4 deletions libc/malloc/Makefile
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Expand Up @@ -4,12 +4,13 @@ COMPILER ?= ia16
LIB ?= out.a

include $(TOPDIR)/libc/$(COMPILER).inc
#CFLAGS += -DL_alloca
#CFLAGS += -DLAZY_FREE
# MCHUNK is word not byte min allocation size
CFLAGS += -DMCHUNK=512
# allocations smaller than MCHUNK words (not bytes) are rounded up,
# larger requests are allocated from heap as is.
CFLAGS += -DMCHUNK=16
#CFLAGS += -DMINALLOC
#CFLAGS += -DLAZY_FREE
#CFLAGS += -DVERBOSE
#CFLAGS += -DL_alloca

# use V7 malloc for heap integrity checking
#OBJS = v7malloc.o calloc.o sbrk.o brk.o
Expand Down
8 changes: 5 additions & 3 deletions libc/malloc/__mini_malloc.c
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Expand Up @@ -8,12 +8,16 @@ void __wcnear *
__mini_malloc(size_t size)
{
mem __wcnear *ptr;
size_t sz;

#if 0
size_t sz;
/* First time round this _might_ be odd, But we won't do that! */
sz = (size_t)sbrk(0);
if(sz & (sizeof(mem) - 1))
sbrk(4 - (sz & (sizeof(mem) - 1)));
#endif

size += sizeof(mem) * 2 - 1; /* Round up and leave space for size field */

/* Minor oops here, sbrk has a signed argument */
if((int)size <= 0 || size > (((unsigned)-1) >> 1) - sizeof(mem) * 3)
Expand All @@ -22,9 +26,7 @@ __mini_malloc(size_t size)
return 0;
}

size += sizeof(mem) * 2 - 1; /* Round up and leave space for size field */
size /= sizeof(mem);

ptr = (mem __wcnear *) sbrk(size * sizeof(mem));
/*if((uintptr_t)ptr == (intptr_t)-1)*/ /* this is better only when not __wcnear */
if ((int)ptr == -1)
Expand Down
6 changes: 5 additions & 1 deletion libc/malloc/malloc.c
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Expand Up @@ -265,10 +265,13 @@ malloc(size_t size)
{
#ifdef MCHUNK
unsigned int alloc;
alloc = sizeof(mem) * (MCHUNK * ((sz + MCHUNK - 1) / MCHUNK) - 1);
if (sz < MCHUNK)
alloc = sizeof(mem) * (MCHUNK * ((sz + MCHUNK - 1) / MCHUNK) - 1);
else alloc = sz * sizeof(mem);
ptr = __mini_malloc(alloc);
if (ptr)
__insert_chunk(ptr - 1);
#if MCHUNK >= 256
else /* Oooo, near end of RAM */
{
unsigned int needed = alloc;
Expand All @@ -283,6 +286,7 @@ malloc(size_t size)
else alloc/=2;
}
}
#endif
ptr = __search_chunk(sz);
if (ptr == 0)
#endif
Expand Down
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