commit 342db04ae71273322f0011384a9ed414df8bdae4 upstream.

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.

Manually backported: show_opcodes() has changed a bit in the meantime. I have manually tested the backport.

Fixes: 7cccf0725cf7 ("x86/dumpstack: Add a show_ip() function") Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20180828154901.112726-1-jannh@google.com Signed-off-by: Jann Horn jannh@google.com --- Since I manually backported this, I have removed all other sign-off/reviewed-by lines. I hope that's correct?

arch/x86/include/asm/stacktrace.h | 2 +- arch/x86/kernel/dumpstack.c | 21 +++++++++++++++------ arch/x86/mm/fault.c | 2 +- 3 files changed, 17 insertions(+), 8 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 666a284116ac..1c65c648cacc 100644 --- a/arch/x86/kernel/dumpstack.c +++ b/arch/x86/kernel/dumpstack.c @@ -91,23 +91,32 @@ 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) { unsigned int code_prologue = OPCODE_BUFSIZE * 2 / 3; u8 opcodes[OPCODE_BUFSIZE]; - u8 *ip; + unsigned long ip; int i; + bool bad_ip;

printk("%sCode: ", loglvl);

- ip = (u8 *)rip - code_prologue; - if (probe_kernel_read(opcodes, ip, OPCODE_BUFSIZE)) { + ip = regs->ip - code_prologue; + + /* + * 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(ip, OPCODE_BUFSIZE, TASK_SIZE_MAX); + + if (bad_ip || probe_kernel_read(opcodes, (u8 *)ip, OPCODE_BUFSIZE)) { pr_cont("Bad RIP value.\n"); return; }

for (i = 0; i < OPCODE_BUFSIZE; i++, ip++) { - if (ip == rip) + if (ip == regs->ip) pr_cont("<%02x> ", opcodes[i]); else pr_cont("%02x ", opcodes[i]); @@ -122,7 +131,7 @@ 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 2aafa6ab6103..d1f1612672c7 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -838,7 +838,7 @@ 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