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Date: Sun, 14 Apr 2024 21:58:37 +0900
From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
To: qiang4.zhang@linux.intel.com
Cc: Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
 linux-trace-kernel@vger.kernel.org, Qiang Zhang <qiang4.zhang@intel.com>,
 Stable@vger.kernel.org
Subject: Re: [PATCH v3] bootconfig: use memblock_free_late to free xbc
 memory to buddy
Message-Id: <20240414215837.de2ce64370c2a2abaeafe46b@kernel.org>
In-Reply-To: <20240414114944.1012359-1-qiang4.zhang@linux.intel.com>
References: <20240414114944.1012359-1-qiang4.zhang@linux.intel.com>
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On Sun, 14 Apr 2024 19:49:45 +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>

Thanks!

> ---
> v3:
> - add NULL pointer check in memblock_free_late() path.
> 
> 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..8841554432d5 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 if (addr)
> +		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>