Patch "x86/amd_nb: Check for invalid SMN reads" has been added to the 4.19-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    x86/amd_nb: Check for invalid SMN reads

to the 4.19-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     x86-amd_nb-check-for-invalid-smn-reads.patch
and it can be found in the queue-4.19 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 3b3b76dcb32862de4d47cf896add50c74c153349
Author: Yazen Ghannam <yazen.ghannam@xxxxxxx>
Date:   Mon Apr 3 16:42:44 2023 +0000

    x86/amd_nb: Check for invalid SMN reads
    
    [ Upstream commit c625dabbf1c4a8e77e4734014f2fde7aa9071a1f ]
    
    AMD Zen-based systems use a System Management Network (SMN) that
    provides access to implementation-specific registers.
    
    SMN accesses are done indirectly through an index/data pair in PCI
    config space. The PCI config access may fail and return an error code.
    This would prevent the "read" value from being updated.
    
    However, the PCI config access may succeed, but the return value may be
    invalid. This is in similar fashion to PCI bad reads, i.e. return all
    bits set.
    
    Most systems will return 0 for SMN addresses that are not accessible.
    This is in line with AMD convention that unavailable registers are
    Read-as-Zero/Writes-Ignored.
    
    However, some systems will return a "PCI Error Response" instead. This
    value, along with an error code of 0 from the PCI config access, will
    confuse callers of the amd_smn_read() function.
    
    Check for this condition, clear the return value, and set a proper error
    code.
    
    Fixes: ddfe43cdc0da ("x86/amd_nb: Add SMN and Indirect Data Fabric access for AMD Fam17h")
    Signed-off-by: Yazen Ghannam <yazen.ghannam@xxxxxxx>
    Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
    Cc: stable@xxxxxxxxxxxxxxx
    Link: https://lore.kernel.org/r/20230403164244.471141-1-yazen.ghannam@xxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/x86/kernel/amd_nb.c b/arch/x86/kernel/amd_nb.c
index 923b4bac96138..ef1fa51ea98e9 100644
--- a/arch/x86/kernel/amd_nb.c
+++ b/arch/x86/kernel/amd_nb.c
@@ -145,7 +145,14 @@ static int __amd_smn_rw(u16 node, u32 address, u32 *value, bool write)
 
 int amd_smn_read(u16 node, u32 address, u32 *value)
 {
-	return __amd_smn_rw(node, address, value, false);
+	int err = __amd_smn_rw(node, address, value, false);
+
+	if (PCI_POSSIBLE_ERROR(*value)) {
+		err = -ENODEV;
+		*value = 0;
+	}
+
+	return err;
 }
 EXPORT_SYMBOL_GPL(amd_smn_read);