Commit-ID: a644cf538b1125410421584c68b2013fdbecbd79
Gitweb: https://git.kernel.org/tip/a644cf538b1125410421584c68b2013fdbecbd79
Author: Jann Horn <ja...@google.com>
AuthorDate: Tue, 28 Aug 2018 17:49:01 +0200
Committer: Thomas Gleixner <t...@linutronix.de>
CommitDate: Thu, 30 Aug 2018 13:10:09 +0200
x86/dumpstack: Don't dump kernel memory based on usermode RIP
show_opcodes() is used both for dumping kernel instructions and for dumping
user instructions. If userspace causes #PF by jumping to a kernel address,
show_opcodes() can be reached with regs->ip controlled by the user,
pointing to kernel code. Make sure that userspace can't trick us into
dumping kernel memory into dmesg.
Fixes: 7cccf0725cf7 ("x86/dumpstack: Add a show_ip() function")
Signed-off-by: Jann Horn <ja...@google.com>
Signed-off-by: Thomas Gleixner <t...@linutronix.de>
Reviewed-by: Kees Cook <keesc...@chromium.org>
Reviewed-by: Borislav Petkov <b...@suse.de>
Cc: "H. Peter Anvin" <h...@zytor.com>
Cc: Andy Lutomirski <l...@kernel.org>
Cc: secur...@kernel.org
Cc: sta...@vger.kernel.org
Link: https://lkml.kernel.org/r/20180828154901.112726-1-ja...@google.com
---
arch/x86/include/asm/stacktrace.h | 2 +-
arch/x86/kernel/dumpstack.c | 15 ++++++++++++---
arch/x86/mm/fault.c | 2 +-
3 files changed, 14 insertions(+), 5 deletions(-)
diff --git a/arch/x86/include/asm/stacktrace.h
b/arch/x86/include/asm/stacktrace.h
index b6dc698f992a..f335aad404a4 100644
--- a/arch/x86/include/asm/stacktrace.h
+++ b/arch/x86/include/asm/stacktrace.h
@@ -111,6 +111,6 @@ static inline unsigned long caller_frame_pointer(void)
return (unsigned long)frame;
}
-void show_opcodes(u8 *rip, const char *loglvl);
+void show_opcodes(struct pt_regs *regs, const char *loglvl);
void show_ip(struct pt_regs *regs, const char *loglvl);
#endif /* _ASM_X86_STACKTRACE_H */
diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index 1596e6bfea6f..605c60b1624f 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -90,14 +90,23 @@ static void printk_stack_address(unsigned long address, int
reliable,
* Thus, the 2/3rds prologue and 64 byte OPCODE_BUFSIZE is just a random
* guesstimate in attempt to achieve all of the above.
*/
-void show_opcodes(u8 *rip, const char *loglvl)
+void show_opcodes(struct pt_regs *regs, const char *loglvl)
{
#define PROLOGUE_SIZE 42
#define EPILOGUE_SIZE 21
#define OPCODE_BUFSIZE (PROLOGUE_SIZE + 1 + EPILOGUE_SIZE)
u8 opcodes[OPCODE_BUFSIZE];
+ u8 *prologue = (u8 *)(regs->ip - PROLOGUE_SIZE);
+ bool bad_ip;
- if (probe_kernel_read(opcodes, rip - PROLOGUE_SIZE, OPCODE_BUFSIZE)) {
+ /*
+ * 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) &&
+ __range_not_ok(prologue, OPCODE_BUFSIZE, TASK_SIZE_MAX);
+
+ if (bad_ip || probe_kernel_read(opcodes, prologue, OPCODE_BUFSIZE)) {
printk("%sCode: Bad RIP value.\n", loglvl);
} else {
printk("%sCode: %" __stringify(PROLOGUE_SIZE) "ph <%02x> %"
@@ -113,7 +122,7 @@ void show_ip(struct pt_regs *regs, const char *loglvl)
#else
printk("%sRIP: %04x:%pS\n", loglvl, (int)regs->cs, (void *)regs->ip);
#endif
- show_opcodes((u8 *)regs->ip, loglvl);
+ show_opcodes(regs, loglvl);
}
void show_iret_regs(struct pt_regs *regs)
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index b9123c497e0a..47bebfe6efa7 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -837,7 +837,7 @@ show_signal_msg(struct pt_regs *regs, unsigned long
error_code,
printk(KERN_CONT "\n");
- show_opcodes((u8 *)regs->ip, loglvl);
+ show_opcodes(regs, loglvl);
}
static void
