[PATCH v2] x86/dumpstack: fix address space casting in show_opcodes()

[Jann Horn]

I sloppily passed a kernel-typed pointer to __range_not_ok(), and sparse
doesn't like that.
Make `prologue` an unsigned long and cast it to a kernel pointer when
calling probe_kernel_read(), just like ~everyone else who calls
probe_kernel_read().
Instead of __range_not_ok() with a cast, call __chk_range_not_ok directly.

Fixes: a644cf538b11 ("x86/dumpstack: Don't dump kernel memory based on usermode 
RIP")
Signed-off-by: Jann Horn <ja...@google.com>
---
 arch/x86/kernel/dumpstack.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index 605c60b1624f..f56895106ccf 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -96,7 +96,7 @@ void show_opcodes(struct pt_regs *regs, const char *loglvl)
 #define EPILOGUE_SIZE 21
 #define OPCODE_BUFSIZE (PROLOGUE_SIZE + 1 + EPILOGUE_SIZE)
        u8 opcodes[OPCODE_BUFSIZE];
-       u8 *prologue = (u8 *)(regs->ip - PROLOGUE_SIZE);
+       unsigned long prologue = regs->ip - PROLOGUE_SIZE;
        bool bad_ip;
 
        /*
@@ -104,9 +104,10 @@ void show_opcodes(struct pt_regs *regs, const char *loglvl)
         * memory by pointing the userspace instruction pointer at it.
         */
        bad_ip = user_mode(regs) &&
-               __range_not_ok(prologue, OPCODE_BUFSIZE, TASK_SIZE_MAX);
+               __chk_range_not_ok(prologue, OPCODE_BUFSIZE, TASK_SIZE_MAX);
 
-       if (bad_ip || probe_kernel_read(opcodes, prologue, OPCODE_BUFSIZE)) {
+       if (bad_ip || probe_kernel_read(opcodes, (u8 *)prologue,
+                                       OPCODE_BUFSIZE)) {
                printk("%sCode: Bad RIP value.\n", loglvl);
        } else {
                printk("%sCode: %" __stringify(PROLOGUE_SIZE) "ph <%02x> %"
-- 
2.19.0.rc1.350.ge57e33dbd1-goog