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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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