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    Subject[PATCH 4.18 039/158] x86/process: Dont mix user/kernel regs in 64bit __show_regs()
    Date
    4.18-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Jann Horn <jannh@google.com>

    commit 9fe6299dde587788f245e9f7a5a1b296fad4e8c7 upstream.

    When the kernel.print-fatal-signals sysctl has been enabled, a simple
    userspace crash will cause the kernel to write a crash dump that contains,
    among other things, the kernel gsbase into dmesg.

    As suggested by Andy, limit output to pt_regs, FS_BASE and KERNEL_GS_BASE
    in this case.

    This also moves the bitness-specific logic from show_regs() into
    process_{32,64}.c.

    Fixes: 45807a1df9f5 ("vdso: print fatal signals")
    Signed-off-by: Jann Horn <jannh@google.com>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Cc: "H. Peter Anvin" <hpa@zytor.com>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Borislav Petkov <bpetkov@suse.de>
    Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Cc: stable@vger.kernel.org
    Link: https://lkml.kernel.org/r/20180831194151.123586-1-jannh@google.com
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/x86/include/asm/kdebug.h | 12 +++++++++++-
    arch/x86/kernel/dumpstack.c | 11 +++--------
    arch/x86/kernel/process_32.c | 4 ++--
    arch/x86/kernel/process_64.c | 12 ++++++++++--
    4 files changed, 26 insertions(+), 13 deletions(-)

    --- a/arch/x86/include/asm/kdebug.h
    +++ b/arch/x86/include/asm/kdebug.h
    @@ -22,10 +22,20 @@ enum die_val {
    DIE_NMIUNKNOWN,
    };

    +enum show_regs_mode {
    + SHOW_REGS_SHORT,
    + /*
    + * For when userspace crashed, but we don't think it's our fault, and
    + * therefore don't print kernel registers.
    + */
    + SHOW_REGS_USER,
    + SHOW_REGS_ALL
    +};
    +
    extern void die(const char *, struct pt_regs *,long);
    extern int __must_check __die(const char *, struct pt_regs *, long);
    extern void show_stack_regs(struct pt_regs *regs);
    -extern void __show_regs(struct pt_regs *regs, int all);
    +extern void __show_regs(struct pt_regs *regs, enum show_regs_mode);
    extern void show_iret_regs(struct pt_regs *regs);
    extern unsigned long oops_begin(void);
    extern void oops_end(unsigned long, struct pt_regs *, int signr);
    --- a/arch/x86/kernel/dumpstack.c
    +++ b/arch/x86/kernel/dumpstack.c
    @@ -155,7 +155,7 @@ static void show_regs_if_on_stack(struct
    * they can be printed in the right context.
    */
    if (!partial && on_stack(info, regs, sizeof(*regs))) {
    - __show_regs(regs, 0);
    + __show_regs(regs, SHOW_REGS_SHORT);

    } else if (partial && on_stack(info, (void *)regs + IRET_FRAME_OFFSET,
    IRET_FRAME_SIZE)) {
    @@ -353,7 +353,7 @@ void oops_end(unsigned long flags, struc
    oops_exit();

    /* Executive summary in case the oops scrolled away */
    - __show_regs(&exec_summary_regs, true);
    + __show_regs(&exec_summary_regs, SHOW_REGS_ALL);

    if (!signr)
    return;
    @@ -416,14 +416,9 @@ void die(const char *str, struct pt_regs

    void show_regs(struct pt_regs *regs)
    {
    - bool all = true;
    -
    show_regs_print_info(KERN_DEFAULT);

    - if (IS_ENABLED(CONFIG_X86_32))
    - all = !user_mode(regs);
    -
    - __show_regs(regs, all);
    + __show_regs(regs, user_mode(regs) ? SHOW_REGS_USER : SHOW_REGS_ALL);

    /*
    * When in-kernel, we also print out the stack at the time of the fault..
    --- a/arch/x86/kernel/process_32.c
    +++ b/arch/x86/kernel/process_32.c
    @@ -59,7 +59,7 @@
    #include <asm/intel_rdt_sched.h>
    #include <asm/proto.h>

    -void __show_regs(struct pt_regs *regs, int all)
    +void __show_regs(struct pt_regs *regs, enum show_regs_mode mode)
    {
    unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L;
    unsigned long d0, d1, d2, d3, d6, d7;
    @@ -85,7 +85,7 @@ void __show_regs(struct pt_regs *regs, i
    printk(KERN_DEFAULT "DS: %04x ES: %04x FS: %04x GS: %04x SS: %04x EFLAGS: %08lx\n",
    (u16)regs->ds, (u16)regs->es, (u16)regs->fs, gs, ss, regs->flags);

    - if (!all)
    + if (mode != SHOW_REGS_ALL)
    return;

    cr0 = read_cr0();
    --- a/arch/x86/kernel/process_64.c
    +++ b/arch/x86/kernel/process_64.c
    @@ -62,7 +62,7 @@
    __visible DEFINE_PER_CPU(unsigned long, rsp_scratch);

    /* Prints also some state that isn't saved in the pt_regs */
    -void __show_regs(struct pt_regs *regs, int all)
    +void __show_regs(struct pt_regs *regs, enum show_regs_mode mode)
    {
    unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L, fs, gs, shadowgs;
    unsigned long d0, d1, d2, d3, d6, d7;
    @@ -87,9 +87,17 @@ void __show_regs(struct pt_regs *regs, i
    printk(KERN_DEFAULT "R13: %016lx R14: %016lx R15: %016lx\n",
    regs->r13, regs->r14, regs->r15);

    - if (!all)
    + if (mode == SHOW_REGS_SHORT)
    return;

    + if (mode == SHOW_REGS_USER) {
    + rdmsrl(MSR_FS_BASE, fs);
    + rdmsrl(MSR_KERNEL_GS_BASE, shadowgs);
    + printk(KERN_DEFAULT "FS: %016lx GS: %016lx\n",
    + fs, shadowgs);
    + return;
    + }
    +
    asm("movl %%ds,%0" : "=r" (ds));
    asm("movl %%cs,%0" : "=r" (cs));
    asm("movl %%es,%0" : "=r" (es));

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