The following commit has been merged into the x86/urgent branch of tip: Commit-ID: 860aaabac8235cfde10fe556aa82abbbe3117888 Gitweb: https://git.kernel.org/tip/860aaabac8235cfde10fe556aa82abbbe3117888 Author: Thomas Gleixner <t...@linutronix.de> AuthorDate: Tue, 17 Nov 2020 21:23:34 +01:00 Committer: Borislav Petkov <b...@suse.de> CommitterDate: Wed, 18 Nov 2020 12:56:29 +01:00
x86/dumpstack: Do not try to access user space code of other tasks sysrq-t ends up invoking show_opcodes() for each task which tries to access the user space code of other processes, which is obviously bogus. It either manages to dump where the foreign task's regs->ip points to in a valid mapping of the current task or triggers a pagefault and prints "Code: Bad RIP value.". Both is just wrong. Add a safeguard in copy_code() and check whether the @regs pointer matches currents pt_regs. If not, do not even try to access it. While at it, add commentary why using copy_from_user_nmi() is safe in copy_code() even if the function name suggests otherwise. Reported-by: Oleg Nesterov <o...@redhat.com> Signed-off-by: Thomas Gleixner <t...@linutronix.de> Signed-off-by: Borislav Petkov <b...@suse.de> Reviewed-by: Borislav Petkov <b...@suse.de> Acked-by: Oleg Nesterov <o...@redhat.com> Tested-by: Borislav Petkov <b...@suse.de> Link: https://lkml.kernel.org/r/20201117202753.667274...@linutronix.de --- arch/x86/kernel/dumpstack.c | 23 +++++++++++++++++++---- 1 file changed, 19 insertions(+), 4 deletions(-) diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c index 25c06b6..97aa900 100644 --- a/arch/x86/kernel/dumpstack.c +++ b/arch/x86/kernel/dumpstack.c @@ -78,6 +78,9 @@ static int copy_code(struct pt_regs *regs, u8 *buf, unsigned long src, if (!user_mode(regs)) return copy_from_kernel_nofault(buf, (u8 *)src, nbytes); + /* The user space code from other tasks cannot be accessed. */ + if (regs != task_pt_regs(current)) + return -EPERM; /* * Make sure userspace isn't trying to trick us into dumping kernel * memory by pointing the userspace instruction pointer at it. @@ -85,6 +88,12 @@ static int copy_code(struct pt_regs *regs, u8 *buf, unsigned long src, if (__chk_range_not_ok(src, nbytes, TASK_SIZE_MAX)) return -EINVAL; + /* + * Even if named copy_from_user_nmi() this can be invoked from + * other contexts and will not try to resolve a pagefault, which is + * the correct thing to do here as this code can be called from any + * context. + */ return copy_from_user_nmi(buf, (void __user *)src, nbytes); } @@ -115,13 +124,19 @@ void show_opcodes(struct pt_regs *regs, const char *loglvl) u8 opcodes[OPCODE_BUFSIZE]; unsigned long prologue = regs->ip - PROLOGUE_SIZE; - if (copy_code(regs, opcodes, prologue, sizeof(opcodes))) { - printk("%sCode: Unable to access opcode bytes at RIP 0x%lx.\n", - loglvl, prologue); - } else { + switch (copy_code(regs, opcodes, prologue, sizeof(opcodes))) { + case 0: printk("%sCode: %" __stringify(PROLOGUE_SIZE) "ph <%02x> %" __stringify(EPILOGUE_SIZE) "ph\n", loglvl, opcodes, opcodes[PROLOGUE_SIZE], opcodes + PROLOGUE_SIZE + 1); + break; + case -EPERM: + /* No access to the user space stack of other tasks. Ignore. */ + break; + default: + printk("%sCode: Unable to access opcode bytes at RIP 0x%lx.\n", + loglvl, prologue); + break; } }
