[PATCH] x86/setup: Avoid OoB E820 lookup when calculating the L1TF safe address

[PATCH] x86/setup: Avoid OoB E820 lookup when calculating the L1TF safe address

[Andrew Cooper]

A number of corner cases (most obviously, no-real-mode and no Multiboot memory
map) can end up with e820_raw.nr_map being 0, at which point the L1TF
calculation will underflow.

Spotted by Coverity.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Wei Liu <wei.liu2@citrix.com>
CC: Roger Pau Monné <roger.pau@citrix.com>
---
 xen/arch/x86/setup.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index 727dad4..8d0f6f1 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -913,7 +913,7 @@ void __init noreturn __start_xen(unsigned long mbi_p)
     /* Sanitise the raw E820 map to produce a final clean version. */
     max_page = raw_max_page = init_e820(memmap_type, &e820_raw);
 
-    if ( !efi_enabled(EFI_BOOT) )
+    if ( !efi_enabled(EFI_BOOT) && e820_raw.nr_map >= 1 )
     {
         /*
          * Supplement the heuristics in l1tf_calculations() by assuming that
-- 
2.1.4


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Re: [PATCH] x86/setup: Avoid OoB E820 lookup when calculating the L1TF safe address

[Roger Pau Monné]

On Thu, Aug 16, 2018 at 04:27:57PM +0100, Andrew Cooper wrote:
> A number of corner cases (most obviously, no-real-mode and no Multiboot memory
> map) can end up with e820_raw.nr_map being 0, at which point the L1TF
> calculation will underflow.
> 
> Spotted by Coverity.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

Thanks.

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Re: [PATCH] x86/setup: Avoid OoB E820 lookup when calculating the L1TF safe address

[Jan Beulich]

>>> On 16.08.18 at 17:27, <andrew.cooper3@citrix.com> wrote:
> A number of corner cases (most obviously, no-real-mode and no Multiboot memory
> map) can end up with e820_raw.nr_map being 0, at which point the L1TF
> calculation will underflow.
> 
> Spotted by Coverity.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

Reviewed-by: Jan Beulich <jbeulich@suse.com>




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Re: [PATCH] x86/setup: Avoid OoB E820 lookup when calculating the L1TF safe address

[Wei Liu]

On Thu, Aug 16, 2018 at 04:27:57PM +0100, Andrew Cooper wrote:
> A number of corner cases (most obviously, no-real-mode and no Multiboot memory
> map) can end up with e820_raw.nr_map being 0, at which point the L1TF
> calculation will underflow.
> 
> Spotted by Coverity.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

Reviewed-by: Wei Liu <wei.liu2@citrix.com>

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