From: Mark Mossberg mark.mossberg@gmail.com
[ Upstream commit 238c91115cd05c71447ea071624a4c9fe661f970 ]
Printing "Bad RIP value" if copy_code() fails can be misleading for userspace pointers, since copy_code() can fail if the instruction pointer is valid but the code is paged out. This is because copy_code() calls copy_from_user_nmi() for userspace pointers, which disables page fault handling.
This is reproducible in OOM situations, where it's plausible that the code may be reclaimed in the time between entry into the kernel and when this message is printed. This leaves a misleading log in dmesg that suggests instruction pointer corruption has occurred, which may alarm users.
Change the message to state the error condition more precisely.
[ bp: Massage a bit. ]
Signed-off-by: Mark Mossberg mark.mossberg@gmail.com Signed-off-by: Borislav Petkov bp@suse.de Link: https://lkml.kernel.org/r/20201002042915.403558-1-mark.mossberg@gmail.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/kernel/dumpstack.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c index 48ce44576947c..ea8d51ec251bb 100644 --- a/arch/x86/kernel/dumpstack.c +++ b/arch/x86/kernel/dumpstack.c @@ -115,7 +115,8 @@ void show_opcodes(struct pt_regs *regs, const char *loglvl) unsigned long prologue = regs->ip - PROLOGUE_SIZE;
if (copy_code(regs, opcodes, prologue, sizeof(opcodes))) { - printk("%sCode: Bad RIP value.\n", loglvl); + printk("%sCode: Unable to access opcode bytes at RIP 0x%lx.\n", + loglvl, prologue); } else { printk("%sCode: %" __stringify(PROLOGUE_SIZE) "ph <%02x> %" __stringify(EPILOGUE_SIZE) "ph\n", loglvl, opcodes,