On Fri, Feb 18, 2022 at 7:28 AM Christoph Hellwig [off-list ref] wrote:

On Wed, Feb 16, 2022 at 02:13:19PM +0100, Arnd Bergmann wrote:

quoted

--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c

@@ -2794,7 +2794,7 @@ perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *re
 static inline int
 valid_user_frame(const void __user *fp, unsigned long size)
 {
-     return (__range_not_ok(fp, size, TASK_SIZE) == 0);
+     return __access_ok(fp, size);
 }

valid_user_frame just need to go away and the following __get_user calls
replaced with normal get_user ones.

As I understand it, that would not work here because get_user() calls
access_ok() rather than __access_ok(), and on x86 that can not be
called in NMI context.

It is a bit odd that x86 is the only architecture that has this check,
but adding
it was clearly intentional, see 7c4788950ba5 ("x86/uaccess, sched/preempt:
Verify access_ok() context").

quoted

diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index 53de044e5654..da534fb7b5c6 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c

@@ -85,7 +85,7 @@ static int copy_code(struct pt_regs *regs, u8 *buf, unsigned long src,
       * Make sure userspace isn't trying to trick us into dumping kernel
       * memory by pointing the userspace instruction pointer at it.
       */
-     if (__chk_range_not_ok(src, nbytes, TASK_SIZE_MAX))
+     if (!__access_ok((void __user *)src, nbytes))
              return -EINVAL;

This one is not needed at all as copy_from_user_nmi already checks the
access range.

Ok, removing this.

quoted

diff --git a/arch/x86/kernel/stacktrace.c b/arch/x86/kernel/stacktrace.c
index 15b058eefc4e..ee117fcf46ed 100644
--- a/arch/x86/kernel/stacktrace.c
+++ b/arch/x86/kernel/stacktrace.c

@@ -90,7 +90,7 @@ copy_stack_frame(const struct stack_frame_user __user *fp,
 {
      int ret;

-     if (__range_not_ok(fp, sizeof(*frame), TASK_SIZE))
+     if (!__access_ok(fp, sizeof(*frame)))
              return 0;

Just switch the __get_user calls below to get_user instead.

Same as the first one, I think we can't do this in NMI context.

         Arnd