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SubjectRe: [PATCH] /dev/mem: Bail out upon SIGKILL when reading memory.
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Date
On 2019/08/25 5:22, Ingo Molnar wrote:
>> So I'd be willing to try that (and then if somebody reports a
>> regression we can make it use "fatal_signal_pending()" instead)
>
> Ok, will post a changelogged patch (unless Tetsuo beats me to it?).

Here is a patch. This patch also tries to fix handling of return code when
partial read/write happened (because we should return bytes processed when
we return due to -EINTR). But asymmetric between read function and write
function looks messy. Maybe we should just make /dev/{mem,kmem} killable
for now, and defer making /dev/{mem,kmem} interruptible till rewrite of
read/write functions.

drivers/char/mem.c | 89 ++++++++++++++++++++++++++++++------------------------
1 file changed, 50 insertions(+), 39 deletions(-)

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index cb8e653..3c6a3c2 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -108,7 +108,7 @@ static ssize_t read_mem(struct file *file, char __user *buf,
ssize_t read, sz;
void *ptr;
char *bounce;
- int err;
+ int err = 0;

if (p != *ppos)
return 0;
@@ -132,8 +132,10 @@ static ssize_t read_mem(struct file *file, char __user *buf,
#endif

bounce = kmalloc(PAGE_SIZE, GFP_KERNEL);
- if (!bounce)
- return -ENOMEM;
+ if (!bounce) {
+ err = -ENOMEM;
+ goto failed;
+ }

while (count > 0) {
unsigned long remaining;
@@ -142,7 +144,7 @@ static ssize_t read_mem(struct file *file, char __user *buf,
sz = size_inside_page(p, count);
cond_resched();
err = -EINTR;
- if (fatal_signal_pending(current))
+ if (signal_pending(current))
goto failed;

err = -EPERM;
@@ -180,14 +182,11 @@ static ssize_t read_mem(struct file *file, char __user *buf,
count -= sz;
read += sz;
}
+failed:
kfree(bounce);

*ppos += read;
- return read;
-
-failed:
- kfree(bounce);
- return err;
+ return read ? read : err;
}

static ssize_t write_mem(struct file *file, const char __user *buf,
@@ -197,6 +196,7 @@ static ssize_t write_mem(struct file *file, const char __user *buf,
ssize_t written, sz;
unsigned long copied;
void *ptr;
+ int err = 0;

if (p != *ppos)
return -EFBIG;
@@ -223,13 +223,16 @@ static ssize_t write_mem(struct file *file, const char __user *buf,

sz = size_inside_page(p, count);
cond_resched();
- if (fatal_signal_pending(current))
- return -EINTR;
+ err = -EINTR;
+ if (signal_pending(current))
+ break;

+ err = -EPERM;
allowed = page_is_allowed(p >> PAGE_SHIFT);
if (!allowed)
- return -EPERM;
+ break;

+ err = -EFAULT;
/* Skip actual writing when a page is marked as restricted. */
if (allowed == 1) {
/*
@@ -238,19 +241,14 @@ static ssize_t write_mem(struct file *file, const char __user *buf,
* by the kernel or data corruption may occur.
*/
ptr = xlate_dev_mem_ptr(p);
- if (!ptr) {
- if (written)
- break;
- return -EFAULT;
- }
+ if (!ptr)
+ break;

copied = copy_from_user(ptr, buf, sz);
unxlate_dev_mem_ptr(p, ptr);
if (copied) {
written += sz - copied;
- if (written)
- break;
- return -EFAULT;
+ break;
}
}

@@ -261,7 +259,7 @@ static ssize_t write_mem(struct file *file, const char __user *buf,
}

*ppos += written;
- return written;
+ return written ? written : err;
}

int __weak phys_mem_access_prot_allowed(struct file *file,
@@ -459,8 +457,10 @@ static ssize_t read_kmem(struct file *file, char __user *buf,
while (low_count > 0) {
sz = size_inside_page(p, low_count);
cond_resched();
- if (fatal_signal_pending(current))
- return -EINTR;
+ if (signal_pending(current)) {
+ err = -EINTR;
+ goto failed;
+ }

/*
* On ia64 if a page has been mapped somewhere as
@@ -468,11 +468,15 @@ static ssize_t read_kmem(struct file *file, char __user *buf,
* by the kernel or data corruption may occur
*/
kbuf = xlate_dev_kmem_ptr((void *)p);
- if (!virt_addr_valid(kbuf))
- return -ENXIO;
+ if (!virt_addr_valid(kbuf)) {
+ err = -ENXIO;
+ goto failed;
+ }

- if (copy_to_user(buf, kbuf, sz))
- return -EFAULT;
+ if (copy_to_user(buf, kbuf, sz)) {
+ err = -EFAULT;
+ goto failed;
+ }
buf += sz;
p += sz;
read += sz;
@@ -483,12 +487,14 @@ static ssize_t read_kmem(struct file *file, char __user *buf,

if (count > 0) {
kbuf = (char *)__get_free_page(GFP_KERNEL);
- if (!kbuf)
- return -ENOMEM;
+ if (!kbuf) {
+ err = -ENOMEM;
+ goto failed;
+ }
while (count > 0) {
sz = size_inside_page(p, count);
cond_resched();
- if (fatal_signal_pending(current)) {
+ if (signal_pending(current)) {
err = -EINTR;
break;
}
@@ -510,6 +516,7 @@ static ssize_t read_kmem(struct file *file, char __user *buf,
}
free_page((unsigned long)kbuf);
}
+ failed:
*ppos = p;
return read ? read : err;
}
@@ -520,6 +527,7 @@ static ssize_t do_write_kmem(unsigned long p, const char __user *buf,
{
ssize_t written, sz;
unsigned long copied;
+ int err = 0;

written = 0;
#ifdef __ARCH_HAS_NO_PAGE_ZERO_MAPPED
@@ -539,8 +547,10 @@ static ssize_t do_write_kmem(unsigned long p, const char __user *buf,

sz = size_inside_page(p, count);
cond_resched();
- if (fatal_signal_pending(current))
- return -EINTR;
+ if (signal_pending(current)) {
+ err = -EINTR;
+ break;
+ }

/*
* On ia64 if a page has been mapped somewhere as uncached, then
@@ -548,15 +558,16 @@ static ssize_t do_write_kmem(unsigned long p, const char __user *buf,
* corruption may occur.
*/
ptr = xlate_dev_kmem_ptr((void *)p);
- if (!virt_addr_valid(ptr))
- return -ENXIO;
+ if (!virt_addr_valid(ptr)) {
+ err = -ENXIO;
+ break;
+ }

copied = copy_from_user(ptr, buf, sz);
if (copied) {
written += sz - copied;
- if (written)
- break;
- return -EFAULT;
+ err = -EFAULT;
+ break;
}
buf += sz;
p += sz;
@@ -565,7 +576,7 @@ static ssize_t do_write_kmem(unsigned long p, const char __user *buf,
}

*ppos += written;
- return written;
+ return written ? written : err;
}

/*
@@ -600,7 +611,7 @@ static ssize_t write_kmem(struct file *file, const char __user *buf,
unsigned long n;

cond_resched();
- if (fatal_signal_pending(current)) {
+ if (signal_pending(current)) {
err = -EINTR;
break;
}
--
1.8.3.1
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