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    Subject[PATCH 5.18 06/11] x86/boot: Wrap literal addresses in absolute_pointer()
    Date
    From: Kees Cook <keescook@chromium.org>

    commit aeb84412037b89e06f45e382f044da6f200e12f8 upstream.

    GCC 11 (incorrectly[1]) assumes that literal values cast to (void *)
    should be treated like a NULL pointer with an offset, and raises
    diagnostics when doing bounds checking under -Warray-bounds. GCC 12
    got "smarter" about finding these:

    In function 'rdfs8',
    inlined from 'vga_recalc_vertical' at /srv/code/arch/x86/boot/video-mode.c:124:29,
    inlined from 'set_mode' at /srv/code/arch/x86/boot/video-mode.c:163:3:
    /srv/code/arch/x86/boot/boot.h:114:9: warning: array subscript 0 is outside array bounds of 'u8[0]' {aka 'unsigned char[]'} [-Warray-bounds]
    114 | asm volatile("movb %%fs:%1,%0" : "=q" (v) : "m" (*(u8 *)addr));
    | ^~~

    This has been solved in other places[2] already by using the recently
    added absolute_pointer() macro. Do the same here.

    [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99578
    [2] https://lore.kernel.org/all/20210912160149.2227137-1-linux@roeck-us.net/

    Signed-off-by: Kees Cook <keescook@chromium.org>
    Signed-off-by: Borislav Petkov <bp@suse.de>
    Reviewed-by: Guenter Roeck <linux@roeck-us.net>
    Link: https://lore.kernel.org/r/20220227195918.705219-1-keescook@chromium.org
    Cc: Jiri Slaby <jirislaby@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/x86/boot/boot.h | 36 ++++++++++++++++++++++++------------
    arch/x86/boot/main.c | 2 +-
    2 files changed, 25 insertions(+), 13 deletions(-)

    --- a/arch/x86/boot/boot.h
    +++ b/arch/x86/boot/boot.h
    @@ -110,66 +110,78 @@ typedef unsigned int addr_t;

    static inline u8 rdfs8(addr_t addr)
    {
    + u8 *ptr = (u8 *)absolute_pointer(addr);
    u8 v;
    - asm volatile("movb %%fs:%1,%0" : "=q" (v) : "m" (*(u8 *)addr));
    + asm volatile("movb %%fs:%1,%0" : "=q" (v) : "m" (*ptr));
    return v;
    }
    static inline u16 rdfs16(addr_t addr)
    {
    + u16 *ptr = (u16 *)absolute_pointer(addr);
    u16 v;
    - asm volatile("movw %%fs:%1,%0" : "=r" (v) : "m" (*(u16 *)addr));
    + asm volatile("movw %%fs:%1,%0" : "=r" (v) : "m" (*ptr));
    return v;
    }
    static inline u32 rdfs32(addr_t addr)
    {
    + u32 *ptr = (u32 *)absolute_pointer(addr);
    u32 v;
    - asm volatile("movl %%fs:%1,%0" : "=r" (v) : "m" (*(u32 *)addr));
    + asm volatile("movl %%fs:%1,%0" : "=r" (v) : "m" (*ptr));
    return v;
    }

    static inline void wrfs8(u8 v, addr_t addr)
    {
    - asm volatile("movb %1,%%fs:%0" : "+m" (*(u8 *)addr) : "qi" (v));
    + u8 *ptr = (u8 *)absolute_pointer(addr);
    + asm volatile("movb %1,%%fs:%0" : "+m" (*ptr) : "qi" (v));
    }
    static inline void wrfs16(u16 v, addr_t addr)
    {
    - asm volatile("movw %1,%%fs:%0" : "+m" (*(u16 *)addr) : "ri" (v));
    + u16 *ptr = (u16 *)absolute_pointer(addr);
    + asm volatile("movw %1,%%fs:%0" : "+m" (*ptr) : "ri" (v));
    }
    static inline void wrfs32(u32 v, addr_t addr)
    {
    - asm volatile("movl %1,%%fs:%0" : "+m" (*(u32 *)addr) : "ri" (v));
    + u32 *ptr = (u32 *)absolute_pointer(addr);
    + asm volatile("movl %1,%%fs:%0" : "+m" (*ptr) : "ri" (v));
    }

    static inline u8 rdgs8(addr_t addr)
    {
    + u8 *ptr = (u8 *)absolute_pointer(addr);
    u8 v;
    - asm volatile("movb %%gs:%1,%0" : "=q" (v) : "m" (*(u8 *)addr));
    + asm volatile("movb %%gs:%1,%0" : "=q" (v) : "m" (*ptr));
    return v;
    }
    static inline u16 rdgs16(addr_t addr)
    {
    + u16 *ptr = (u16 *)absolute_pointer(addr);
    u16 v;
    - asm volatile("movw %%gs:%1,%0" : "=r" (v) : "m" (*(u16 *)addr));
    + asm volatile("movw %%gs:%1,%0" : "=r" (v) : "m" (*ptr));
    return v;
    }
    static inline u32 rdgs32(addr_t addr)
    {
    + u32 *ptr = (u32 *)absolute_pointer(addr);
    u32 v;
    - asm volatile("movl %%gs:%1,%0" : "=r" (v) : "m" (*(u32 *)addr));
    + asm volatile("movl %%gs:%1,%0" : "=r" (v) : "m" (*ptr));
    return v;
    }

    static inline void wrgs8(u8 v, addr_t addr)
    {
    - asm volatile("movb %1,%%gs:%0" : "+m" (*(u8 *)addr) : "qi" (v));
    + u8 *ptr = (u8 *)absolute_pointer(addr);
    + asm volatile("movb %1,%%gs:%0" : "+m" (*ptr) : "qi" (v));
    }
    static inline void wrgs16(u16 v, addr_t addr)
    {
    - asm volatile("movw %1,%%gs:%0" : "+m" (*(u16 *)addr) : "ri" (v));
    + u16 *ptr = (u16 *)absolute_pointer(addr);
    + asm volatile("movw %1,%%gs:%0" : "+m" (*ptr) : "ri" (v));
    }
    static inline void wrgs32(u32 v, addr_t addr)
    {
    - asm volatile("movl %1,%%gs:%0" : "+m" (*(u32 *)addr) : "ri" (v));
    + u32 *ptr = (u32 *)absolute_pointer(addr);
    + asm volatile("movl %1,%%gs:%0" : "+m" (*ptr) : "ri" (v));
    }

    /* Note: these only return true/false, not a signed return value! */
    --- a/arch/x86/boot/main.c
    +++ b/arch/x86/boot/main.c
    @@ -33,7 +33,7 @@ static void copy_boot_params(void)
    u16 cl_offset;
    };
    const struct old_cmdline * const oldcmd =
    - (const struct old_cmdline *)OLD_CL_ADDRESS;
    + absolute_pointer(OLD_CL_ADDRESS);

    BUILD_BUG_ON(sizeof(boot_params) != 4096);
    memcpy(&boot_params.hdr, &hdr, sizeof(hdr));

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