diff options
authorJann Horn <jannh@google.com>2018-08-28 17:49:01 +0200
committerThomas Gleixner <tglx@linutronix.de>2018-08-31 17:08:22 +0200
commit342db04ae71273322f0011384a9ed414df8bdae4 (patch)
parent26e609eccd37967d3681662433086894830c5d62 (diff)
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 <jannh@google.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Kees Cook <keescook@chromium.org> Reviewed-by: Borislav Petkov <bp@suse.de> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: security@kernel.org Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20180828154901.112726-1-jannh@google.com
3 files changed, 15 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..f56895106ccf 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -90,14 +90,24 @@ 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
u8 opcodes[OPCODE_BUFSIZE];
+ unsigned long prologue = 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) &&
+ __chk_range_not_ok(prologue, OPCODE_BUFSIZE, TASK_SIZE_MAX);
+ if (bad_ip || probe_kernel_read(opcodes, (u8 *)prologue,
printk("%sCode: Bad RIP value.\n", loglvl);
} else {
printk("%sCode: %" __stringify(PROLOGUE_SIZE) "ph <%02x> %"
@@ -113,7 +123,7 @@ void show_ip(struct pt_regs *regs, const char *loglvl)
printk("%sRIP: %04x:%pS\n", loglvl, (int)regs->cs, (void *)regs->ip);
- 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