The following commit has been merged into the x86/urgent branch of tip:
Commit-ID: d181d2da0141371bbc360eaea78719203e165e1c
Gitweb: https://git.kernel.org/tip/d181d2da0141371bbc360eaea78719203e165e1c
Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate: Wed, 22 Jul 2020 10:39:54 +02:00
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Wed, 22 Jul 2020 23:47:48 +02:00
x86/dumpstack: Dump user space code correctly again
H.J. reported that post 5.7 a segfault of a user space task does not longer
dump the Code bytes when /proc/sys/debug/exception-trace is enabled. It
prints 'Code: Bad RIP value.' instead.
This was broken by a recent change which made probe_kernel_read() reject
non-kernel addresses.
Update show_opcodes() so it retrieves user space opcodes via
copy_from_user_nmi().
Fixes: 98a23609b103 ("maccess: always use strict semantics for probe_kernel_read")
Reported-by: H.J. Lu <hjl.tools@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/87h7tz306w.fsf@xxxxxxxxxxxxxxxxxxxxxxx
---
arch/x86/kernel/dumpstack.c | 27 +++++++++++++++++----------
1 file changed, 17 insertions(+), 10 deletions(-)
diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index b037cfa..7401cc1 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -71,6 +71,22 @@ static void printk_stack_address(unsigned long address, int reliable,
printk("%s %s%pB\n", log_lvl, reliable ? "" : "? ", (void *)address);
}
+static int copy_code(struct pt_regs *regs, u8 *buf, unsigned long src,
+ unsigned int nbytes)
+{
+ if (!user_mode(regs))
+ return copy_from_kernel_nofault(buf, (u8 *)src, nbytes);
+
+ /*
+ * 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))
+ return -EINVAL;
+
+ return copy_from_user_nmi(buf, (void __user *)src, nbytes);
+}
+
/*
* There are a couple of reasons for the 2/3rd prologue, courtesy of Linus:
*
@@ -97,17 +113,8 @@ void show_opcodes(struct pt_regs *regs, const char *loglvl)
#define OPCODE_BUFSIZE (PROLOGUE_SIZE + 1 + EPILOGUE_SIZE)
u8 opcodes[OPCODE_BUFSIZE];
unsigned long prologue = regs->ip - PROLOGUE_SIZE;
- bool bad_ip;
-
- /*
- * Make sure userspace isn't trying to trick us into dumping kernel
- * memory by pointing the userspace instruction pointer at it.
- */
- bad_ip = user_mode(regs) &&
- __chk_range_not_ok(prologue, OPCODE_BUFSIZE, TASK_SIZE_MAX);
- if (bad_ip || copy_from_kernel_nofault(opcodes, (u8 *)prologue,
- OPCODE_BUFSIZE)) {
+ if (copy_code(regs, opcodes, prologue, sizeof(opcodes))) {
printk("%sCode: Bad RIP value.\n", loglvl);
} else {
printk("%sCode: %" __stringify(PROLOGUE_SIZE) "ph <%02x> %"
|