Re: [PATCH v2] bootconfig: use memblock_free_late to free xbc memory to buddy

Masami Hiramatsu
2024-04-12T13:18:24Z

On Fri, 12 Apr 2024 18:49:41 +0800
qiang4.zhang@linux.intel.com wrote:

> From: Qiang Zhang <qiang4.zhang@intel.com>
>
> On the time to free xbc memory in xbc_exit(), memblock may has handed
> over memory to buddy allocator. So it doesn't make sense to free memory
> back to memblock. memblock_free() called by xbc_exit() even causes UAF bugs
> on architectures with CONFIG_ARCH_KEEP_MEMBLOCK disabled like x86.
> Following KASAN logs shows this case.
>
> This patch fixes the xbc memory free problem by calling memblock_free()
> in early xbc init error rewind path and calling memblock_free_late() in
> xbc exit path to free memory to buddy allocator.
>
> [ 9.410890] ==================================================================
> [ 9.418962] BUG: KASAN: use-after-free in memblock_isolate_range+0x12d/0x260
> [ 9.426850] Read of size 8 at addr ffff88845dd30000 by task swapper/0/1
>
> [ 9.435901] CPU: 9 PID: 1 Comm: swapper/0 Tainted: G U 6.9.0-rc3-00208-g586b5dfb51b9 #5
> [ 9.446403] Hardware name: Intel Corporation RPLP LP5 (CPU:RaptorLake)/RPLP LP5 (ID:13), BIOS IRPPN02.01.01.00.00.19.015.D-00000000 Dec 28 2023
> [ 9.460789] Call Trace:
> [ 9.463518] <TASK>
> [ 9.465859] dump_stack_lvl+0x53/0x70
> [ 9.469949] print_report+0xce/0x610
> [ 9.473944] ? __virt_addr_valid+0xf5/0x1b0
> [ 9.478619] ? memblock_isolate_range+0x12d/0x260
> [ 9.483877] kasan_report+0xc6/0x100
> [ 9.487870] ? memblock_isolate_range+0x12d/0x260
> [ 9.493125] memblock_isolate_range+0x12d/0x260
> [ 9.498187] memblock_phys_free+0xb4/0x160
> [ 9.502762] ? __pfx_memblock_phys_free+0x10/0x10
> [ 9.508021] ? mutex_unlock+0x7e/0xd0
> [ 9.512111] ? __pfx_mutex_unlock+0x10/0x10
> [ 9.516786] ? kernel_init_freeable+0x2d4/0x430
> [ 9.521850] ? __pfx_kernel_init+0x10/0x10
> [ 9.526426] xbc_exit+0x17/0x70
> [ 9.529935] kernel_init+0x38/0x1e0
> [ 9.533829] ? _raw_spin_unlock_irq+0xd/0x30
> [ 9.538601] ret_from_fork+0x2c/0x50
> [ 9.542596] ? __pfx_kernel_init+0x10/0x10
> [ 9.547170] ret_from_fork_asm+0x1a/0x30
> [ 9.551552] </TASK>
>
> [ 9.555649] The buggy address belongs to the physical page:
> [ 9.561875] page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x1 pfn:0x45dd30
> [ 9.570821] flags: 0x200000000000000(node=0|zone=2)
> [ 9.576271] page_type: 0xffffffff()
> [ 9.580167] raw: 0200000000000000 ffffea0011774c48 ffffea0012ba1848 0000000000000000
> [ 9.588823] raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000
> [ 9.597476] page dumped because: kasan: bad access detected
>
> [ 9.605362] Memory state around the buggy address:
> [ 9.610714] ffff88845dd2ff00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> [ 9.618786] ffff88845dd2ff80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> [ 9.626857] >ffff88845dd30000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> [ 9.634930] ^
> [ 9.638534] ffff88845dd30080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> [ 9.646605] ffff88845dd30100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> [ 9.654675] ==================================================================
>
> Cc: Stable@vger.kernel.org
> Signed-off-by: Qiang Zhang <qiang4.zhang@intel.com>

Looks good to me.

Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Also,

Fixes: 40caa127f3c7 ("init: bootconfig: Remove all bootconfig data when the init memory is removed")

Let me pick this for bootconfig/fixes.

Thanks!

> ---
> v2:
> - add an early flag in xbc_free_mem() to free memory back to memblock in
> xbc_init error path or put memory to buddy allocator in normal xbc_exit.
>
> ---
> include/linux/bootconfig.h | 7 ++++++-
> lib/bootconfig.c | 19 +++++++++++--------
> 2 files changed, 17 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/bootconfig.h b/include/linux/bootconfig.h
> index e5ee2c694401..3f4b4ac527ca 100644
> --- a/include/linux/bootconfig.h
> +++ b/include/linux/bootconfig.h
> @@ -288,7 +288,12 @@ int __init xbc_init(const char *buf, size_t size, const char **emsg, int *epos);
> int __init xbc_get_info(int *node_size, size_t *data_size);
>
> /* XBC cleanup data structures */
> -void __init xbc_exit(void);
> +void __init _xbc_exit(bool early);
> +
> +static inline void xbc_exit(void)
> +{
> + _xbc_exit(false);
> +}
>
> /* XBC embedded bootconfig data in kernel */
> #ifdef CONFIG_BOOT_CONFIG_EMBED
> diff --git a/lib/bootconfig.c b/lib/bootconfig.c
> index c59d26068a64..f9a45adc6307 100644
> --- a/lib/bootconfig.c
> +++ b/lib/bootconfig.c
> @@ -61,9 +61,12 @@ static inline void * __init xbc_alloc_mem(size_t size)
> return memblock_alloc(size, SMP_CACHE_BYTES);
> }
>
> -static inline void __init xbc_free_mem(void *addr, size_t size)
> +static inline void __init xbc_free_mem(void *addr, size_t size, bool early)
> {
> - memblock_free(addr, size);
> + if (early)
> + memblock_free(addr, size);
> + else
> + memblock_free_late(__pa(addr), size);
> }
>
> #else /* !__KERNEL__ */
> @@ -73,7 +76,7 @@ static inline void *xbc_alloc_mem(size_t size)
> return malloc(size);
> }
>
> -static inline void xbc_free_mem(void *addr, size_t size)
> +static inline void xbc_free_mem(void *addr, size_t size, bool early)
> {
> free(addr);
> }
> @@ -904,13 +907,13 @@ static int __init xbc_parse_tree(void)
> * If you need to reuse xbc_init() with new boot config, you can
> * use this.
> */
> -void __init xbc_exit(void)
> +void __init _xbc_exit(bool early)
> {
> - xbc_free_mem(xbc_data, xbc_data_size);
> + xbc_free_mem(xbc_data, xbc_data_size, early);
> xbc_data = NULL;
> xbc_data_size = 0;
> xbc_node_num = 0;
> - xbc_free_mem(xbc_nodes, sizeof(struct xbc_node) * XBC_NODE_MAX);
> + xbc_free_mem(xbc_nodes, sizeof(struct xbc_node) * XBC_NODE_MAX, early);
> xbc_nodes = NULL;
> brace_index = 0;
> }
> @@ -963,7 +966,7 @@ int __init xbc_init(const char *data, size_t size, const char **emsg, int *epos)
> if (!xbc_nodes) {
> if (emsg)
> *emsg = "Failed to allocate bootconfig nodes";
> - xbc_exit();
> + _xbc_exit(true);
> return -ENOMEM;
> }
> memset(xbc_nodes, 0, sizeof(struct xbc_node) * XBC_NODE_MAX);
> @@ -977,7 +980,7 @@ int __init xbc_init(const char *data, size_t size, const char **emsg, int *epos)
> *epos = xbc_err_pos;
> if (emsg)
> *emsg = xbc_err_msg;
> - xbc_exit();
> + _xbc_exit(true);
> } else
> ret = xbc_node_num;
>
> --
> 2.39.2
>

--
Masami Hiramatsu (Google) <mhiramat@kernel.org>